42nd International Symposium on Lattice Field Theory (Lattice 2025)

2 Nov 2025, 16:00 → 8 Nov 2025, 14:30 Asia/Kolkata

Homi Bhabha Auditorium (TIFR Mumbai)

Nilmani Mathur

The 42nd International Symposium on Lattice Field Theory (Lattice 2025) will be held at the Tata Institute of Fundamental Research (TIFR), Mumbai, India, November 2-8, 2025. This annual conference brings together scientists from around the world who specialize in the numerical evaluation of quantum field theories. The conference primarily focuses on the latest theoretical and algorithm developments in Lattice Gauge Theory,  particularly in Quantum Chromodynamics (QCD). Given the pivotal role of high-performance computing in these simulations, discussions on software advancements, hardware innovations, and algorithmic developments have always been an integral part of the conference. The conference now also encompasses areas such as machine architectures, AI/ML applications in physics, and algorithm development for quantum computing.

The main conference venue will be the Homi Bhabha Auditorium, TIFR.

Conference website: https://indico.global/e/lattice2025

HandbookLattice2025.pdf

Lattice_2025_Poster.pdf

tifr_map.pdf

Sunday 2 November

Reception and registration with high tea

Monday 3 November

Plenary session: Opening Ceremony followed by Plenary Talks

Convener: Andreas Kronfeld (Fermi National Accelerator Lab. (US))

1 Opening remarks

2 Muon g-2: hadronic contributions with lattice QCD

The Standard Model prediction for the anomalous magnetic moment of the muon, presented in the 2025 White Paper of the Muon g-2 Theory Initiative, is based on consolidated lattice averages for the two leading hadronic contributions, hadronic vacuum polarization and hadronic light-by-light. In this talk, I review the results from lattice QCD+QED calculations that were used in these averages and discuss their construction in the White Paper. I also review the remarkable progress in lattice calculations of these quantities since then, and conclude with an outlook.

Speaker: Aida El-Khadra (University of Illinois Urbana-Champaign)

3 Data-driven methods for the hadronic contributions to the muon $g-2$: status and perspectives

After the final release of results from the Fermilab Muon $g-2$
experiment, the experimental world average has reached a precision of
124 parts per billion, allowing for a Standard-Model precision test
below 0.2 parts per million if the theory prediction could be evaluated
at a similar level of precision as the experimental result. At present,
this is not the case, diluting the sensitivity to potential
beyond-the-Standard-Model degrees of freedom. Apart from improved
lattice-QCD calculations, a number of ongoing efforts using data-driven
methods aim at improving the current puzzling situation, to ideally
arrive at two independent determinations of the critical hadronic
contributions and thereby increase confidence in the resulting
Standard-Model prediction. In the talk, I will give a summary of the
current status, both for hadronic vacuum polarization and hadronic
light-by-light scattering, discuss the most pressing challenges, and
give an overview over the various avenues for future improvements.

Speaker: Martin Hoferichter

10:45 Coffee break

Plenary session

Convener: Stephen Sharpe (University of Washington)

4 BMW/DMZ calculation of the hadronic vacuum polarisation for the muon magnetic moment

For twenty years, a persistent discrepancy between experimental
measurements and theoretical calculations of the muon anomalous magnetic
moment have provided tantalising hints of new physics. In recent years,
improvements to the experimental precision have appeared to make the
tension stronger and stronger. However, at the same time, our lattice calculation overturned the theoretical consensus, completely eliminating the tension. I will present the latest results from the Budapest-Marseille-Wuppertal (BMW) and DMZ collaborations, with a determination of the hadronic vacuum polarisation contribution to a precision of 0.45%.

Speaker: Finn Stokes (The University of Adelaide)

5 Hadron spectroscopy and interactions

In recent years, lattice QCD calculations of hadron spectroscopy have concentrated on resonances and shallow bound states detected via poles in two- and three-hadron scattering amplitudes. Hadron interactions have therefore become a key focus. The primary tools for this are finite-volume spectroscopy and finite-volume quantization conditions. I will review the current state of the art and recent developments in the field.

Speaker: Jeremy Green (DESY, Zeuthen)

6 Nucleon-nucleon interactions: past, present, and future

Grounding nuclear physics in the Standard Model has been a longstanding goal for many in the lattice QCD community. The combined issues of signal-to-noise and difficulties associated with quantifying multi-hadronic interactions have required enormous efforts and improvements in computational techniques and analysis over the course of decades. Now, we have reached a time when computational and algorithmic advancements are finally allowing for faithful, consistent results for two-nucleon calculations across multiple collaborations using different approaches, paving the way for full calculations at the physical point. In this talk, I will focus on calculations of nucleon-nucleon interactions, highlighting the issues faced, the current status of the field, and the potential for future calculations in the realm of nuclear physics.

Speaker: Amy Nicholson (UNC Chapel Hill)

13:00 Lunch break

Algorithms and artificial intelligence

7 Testing two-level sampling for fermionic observables

We present recent progress in combining a two-level sampling algorithm with distillation techniques to compute fermionic observables. The method relies on expressing the quark propagator as a series of domain-local contributions, each depending only on the gauge links in a restricted region, which can then be estimated independently with a two-level sampling strategy. This enables an exponential gain in the signal-to-noise of fermionic correlators as the number of submeasurements increases. We test the method on pure gauge ensembles and we compute both the first two terms in the series with a two-level sampling. We will show results for different iso-singlet observables and outline prospects for applying the two-level algorithm to dynamical QCD simulations.

Speaker: Lorenzo Barca (DESY)

8 Applying the Worldvolume Hybrid Monte Carlo method to lattice gauge theories

The numerical sign problem remains one of the central challenges in first-principles simulations. The Worldvolume Hybrid Monte Carlo (WV-HMC) has recently emerged as a reliable and computationally efficient algorithm, and, crucially, avoids the ergodicity issues inherent in Lefschetz-thimble approaches. In this talk, after outlining the key ideas behind WV-HMC, I will present its extension to group-manifold configuration spaces and report on recent progress in its application to lattice gauge theories. [Based on arXiv:2506.12002 [hep-lat] and ongoing work.]

Speaker: Masafumi Fukuma (Kyoto University)

9 Analyzing the two-dimensional doped Hubbard model with the Worldvolume HMC method

We apply the Worldvolume Hybrid Monte Carlo (WV-HMC) method [arXiv:2012.08468] to the two-dimensional doped Hubbard model, a system structurally similar to finite-density QCD. This model is known to suffer from a severe sign problem at low temperatures and away from half filling (doped), which renders traditional Determinantal Quantum Monte Carlo (DQMC) approaches ineffective. We demonstrate that WV-HMC enables the computation of physical observables with well-controlled statistical errors, even in parameter regimes where DQMC fails severely. [Based on arXiv:2507.23748, 2508.02659, and ongoing work.]

Speaker: Yusuke Namekawa (Fukuyama University)

10 Multigrid low-mode averaging for Wilson fermions

We develop a generalization of low-mode averaging in which the number of low quark modes of the Dirac operator required for a constant variance reduction can be kept independent of the volume by exploiting their local coherence. Typically in lattice QCD simulations, the benefit of translation averaging quark propagators over the space-time volume is spoiled by large fluctuations introduced by the approximations needed to estimate the average. For quark-line connected diagrams at large separations, most of this additional variance can be efficiently suppressed by the introduction of hierarchical subspaces, thanks to the reduced size of the coarse grid operators that act within the subspaces. In this work, we investigate the contributions to the variance of the isovector vector current correlator with $N_f=2$ non-perturbatively $O(a)$-improved Wilson fermions on lattices approximately of size $L = 2, 3$ and $4$ fm. The numerical results obtained confirm that the variance decreases as the volume is increased when a multigrid decomposition is used with a fixed number of low modes. While the proposed decomposition can be applied to any quark propagator, it is expected to be especially effective for quark-line connected diagrams at large separations, for example, the isovector contribution to the hadronic vacuum polarization or baryonic correlators.

Speaker: Roman Gruber

11 AdvNF and ScoreNF for reliable and efficient sampling of lattices

Unnormalized probability distributions are fundamental in modelling complex physical systems, especially in lattice field theory. Traditionally, Markov Chain Monte Carlo (MCMC) methods used to study these systems often exhibit slow convergence, critical slowing down, and poor mixing, resulting in highly correlated samples. Machine learning–based sampling approaches, such as normalising flows (NFs), are being extensively used in conjunction with the Metropolis-Hastings algorithm to produce unbiased samples. This talk discusses several shortcomings of NFs and some of our solutions for them. Often, especially in high-dimensional lattices, the target distributions are multi-modal, i.e., they have multiple high-probability regions (also known as modes) separated by low-probability barriers. In NF, reverse KL training leads to mode collapse (learning only a few modes), whereas forward KL training induces mode-covering behaviour (producing samples from low-probability regions). Moreover, forward KL training relies on MCMC-generated samples, which increases the computational costs. We propose two approaches: an adversarial learning approach (AdvNF) and a score-based learning approach (ScoreNF), demonstrating their effectiveness and efficiency on multiple benchmark datasets, including the mixture of Gaussians, the XY model, and the scalar φ⁴ theory.

Speakers: Vikas Kanaujia (IIT Kanpur), Vipu Arora (IIT Kanpur and KU Leuven)

Hadronic and nuclear spectrum and interactions

Convener: Urs Heller (Physical Review D, American Physical Society)

12 Precisely determining the ground state mass of Spin-3/2 $\Omega_{ccc}$ baryon from Lattice QCD

We present the most precise determination to date of the ground-state masses of the triply charmed baryons with both parities, obtained by continuum extrapolation from two complementary lattice setups and thus fully addressing the systematic uncertainties. The calculations are performed on six $N_f=2+1+1$ HISQ ensembles generated by the MILC collaboration. In the valence sector we use HISQ fermions as well as overlap fermions. Our prediction for the mass of the lowest two triply charmed spin-3/2 baryons are: $M_{\Omega_{ccc}} (3/2^{+}) = 4793 (5) \left(^{+11}_{-8}\right)$ MeV, and $M_{\Omega_{ccc}} (3/2^{-}) = 5094 (12) \left(^{+19}_{-17}\right)$ MeV.

Speaker: Navdeep Singh Dhindsa (Tata Institute of Fundamental Research, Mumbai)

13 Studying heavy hadrons with relativistic quarks

We present preliminary lattice QCD results for the ground-state spectrum of hadrons containing bottom, charm, and strange quarks. Using relativistic highly improved staggered quarks (HISQ) for all three flavors—bottom, charm, and strange—on $2{+}1{+}1$ ensembles, we compute meson and spin-$3/2$ baryon masses. While some states have been observed experimentally, much in the bottom sector remains uncharted, making lattice predictions essential for guiding future experimental searches. We observe that the taste splittings of baryons across all flavor channels are consistent within statistical errors. Our results show good agreement of baryon masses between calculations using relativistic bottom quarks and previous studies employing non-relativistic formulations.

Speaker: Archana Radhakrishnan

14 Precision charmonium spectroscopy on CLS ensembles: an update

The masses of the lowest charmonium states are determined on a set of over 50 coordinated lattice simulations (CLS) gauge ensembles with $N_f=2+1$ sea quark flavours of non-perturbatively improved Wilson fermions. The inverse lattice spacing is varied from about 2 GeV up to more than 5 GeV, whereas various combinations of pion and kaon masses cover the quark mass plane, with the pion mass ranging from 420 MeV down to 130 MeV. This enables controlled continuum limit and quark mass extrapolations and allows the impact of the neglected charm quark annihilation diagrams and of the electromagnetic interaction to be assessed.

Speaker: Gunnar Bali (Universität Regensburg)

15 Heavy hadron spectrum from 2+1+1 flavor MILC lattices

We study the mass spectra of heavy hadrons containing one or more bottom quarks, along with their hyperfine splittings and mass differences, using MILC's Nf = 2+1+1 HISQ gauge ensembles at three lattice spacings. To simulate the valence quark flavors, we employ a combination of lattice actions adapted to their masses: the NRQCD action is used for bottom quarks, the anisotropic Clover action is adopted for charm quarks, and the $\mathcal{O}(a)$-improved Wilson-Clover action is used for strange and lighter (up/down) quarks. The strange quark masses are tuned to match the lattice value for the fictitious $\eta_s (\bar ss)$ pseudoscalar meson mass with 688.5 MeV. The bare bottom quark mass is tuned by equating the kinetic mass, while the bare charm quark mass is tuned using the pole mass of the respective heavy-strange meson with the physical values. Heavy hadron operators with at least one bottom quark are constructed by considering all possible combinations with charm, strange, and light quarks. We investigate ground state masses for all different bottom mesons and bottom baryons with various quantum numbers.

Speaker: Sabiar Shaikh (National Institute of Science Education and Research, Bhubaneswar)

16 Mixing of light meson and charmonium flavor singlets in $N_f = 3 + 1$ QCD

We investigate the mixing between S-wave flavor-singlet light meson and charmonium operators in two $N_f = 3 + 1$ ensembles at different pion masses ($m_{\pi} \approx 420, 800$ MeV). By solving a GEVP we find both types of operators have non-zero overlaps with all states we look at. We also compare the resulting spectrum with the one coming from separate GEVPs including either only light meson or only charmonium operators and quantify the effects of the mixing on the hyperfine splitting. The largest effect we observe is a decrease of the $\eta_c$ mass by 39(24) MeV. Finally, we show preliminary results of the mixing between both types of operators with glueball ones as a first step to further extend our operator basis.

Speaker: Juan Andres Urrea Nino (Trinity College Dublin)

Hadronic contribution to the magnetic moment of muon

Convener: Finn Stokes (The University of Adelaide)

17 Lattice determination of the higher-order hadronic vacuum polarisation contributions to the muon g-2.

We compute the next-to-leading order (NLO) hadronic vacuum polarisation (HVP) contribution to the muon anomalous magnetic moment, $a_\mu^{\mathrm{hvp}}[\mathrm{NLO}]$ in lattice QCD. The kernel functions required for the three NLO diagrams are considered in the time-momentum representation (TMR), following the methodology of Balzani, Laporta, and Passera. For higher-order (HO) corrections involving additional photon or lepton lines, we derive analytical expansions at short Euclidean times and numerical expansions at large times. The NLO contribution with two QCD insertions is analytically integrated, and the resulting expression is then expanded across different regions of the Euclidean time plane. We combine these kernels with vector two-point correlation functions computed on over 30 CLS ensembles with Wilson fermions. To control discretisation effects, we apply two different $\mathcal{O}(a)$ improvement schemes for the vector current, each using two discretisations, and employ time-window techniques to isolate the continuum-dominant contributions. On each ensemble, we apply finite-volume corrections using both the Hansen-Patella and Meyer-Lellouch-Lüscher approaches to match to a common reference volume, supplemented by a final correction step to infinite volume in the continuum limit. A combined chiral and continuum extrapolation yields our final result for $a_\mu^{\mathrm{hvp}}[\mathrm{NLO}]$.

Speaker: Arnau Beltran (JGU Mainz)

18 The hadronic contribution to the running of $\alpha$ and the electroweak mixing angle.

We present an updated determination of the hadronic vacuum polarization contribution to the running of the electromagnetic coupling $\Delta\alpha_{\mathrm{had}}^{(5)}(-Q^2)$, and of the electroweak mixing angle in the space-like momentum range up to $ 12 \ \mathrm{GeV}^2$. Using $N_f=2+1$ CLS ensembles at five lattice spacings and several pion masses, including the physical point, we achieve a significantly enhanced precision over our previous result. A refined analysis strategy based on telescopic series and a new family of kernel functions enables a clean separation of distinct Euclidean regions, disentangling strong cutoff effects at short distances from the pronounced chiral dependence at larger ones. Employing the Euclidean splitting technique, we convert our lattice results into an ab initio estimate of $\Delta\alpha_{\mathrm{had}}^{(5)}(M_Z^2)$. A detailed comparison with results from other lattice calculations and phenomenology is performed.

Speaker: Alessandro Conigli

19 Light Quark Connected Hadronic Vacuum Polarization Contribution to muon anomaly via Sparsened Meson Fields

We present an update on our determination of the light-quark connected contribution to the hadronic vacuum polarization (HVP) of the muon anomalous magnetic moment, $a_\mu$, on a finer lattice with 2+1+1 highly-improved staggered quark (HISQ) ensemble from the MILC collaboration with physical pion mass, 0.042 fm lattice spacing, and size $144^3 \times 288$ sites. Within the low-mode averaging (LMA) framework, the HVP correlator is decomposed into low-low (LL), high-low (HL), low-high (LH) and high-high (HH) components. Since the LL part dominates the total statistical uncertainty but is also the most computationally expensive to evaluate, we implement a sparsening strategy to construct the meson fields efficiently. This approach significantly reduces the computational cost while preserving signal quality. By combining the sparsened LL contribution with HL and HH components, we achieve an improved determination of the light-quark connected HVP contribution to $a_\mu$.

Speaker: Vaishakhi Moningi (University of Connecticut)

20 RBC/UKQCD HVP status and overview

I present the current status of the RBC/UKQCD HVP program and will give an outlook on the remaining steps for matching the Fermilab E989 experimental precision.

Speaker: Christoph Lehner (University of Regensburg)

21 RBC/UKQCD HVP isospin breaking corrections

In the recent muon g-2 white paper update, the hadronic vacuum polarization (HVP) contribution⸺which dominates the theoretical uncertainty⸺is evaluated as an average of different lattice QCD calculations. Since lattice simulations are mostly carried out in isospin symmetric QCD, corrections due to the mass difference of the up and down quarks and the coupling to photons have to be accounted for. These isospin breaking effects are of order 1% and can be treated as corrections to the result for the HVP contribution in isospin symmetric QCD. In the current estimate of the HVP contribution, these effects are a large source of uncertainty due to the extensive computational cost to compute all occurring Wick contractions and degrading signal-to-noise behaviour especially for quark disconnected diagrams.

I present the current status of the calculation of isospin breaking corrections in the HVP contribution for the RBC/UKQCD Collaboration. We use a dataset of stochastically sampled all-to-all propagators to construct all necessary Wick contractions for the electromagnetic and strong isospin breaking effects. We employ different versions of QED on the lattice, such as QED_L, QED_r and QED_\infty to check for consistency.

Speaker: Julian Parrino (University of Regensburg)

QCD at nonzero temperature and density

22 On the lattice phase structure of massless many-flavour QCD

The properties of QCD with massless quarks, particularly the chiral phase transition, have important implications for our understanding of QCD at the physical point. Once the number of massless fermions exceeds a critical value, $N_f^*$​, QCD enters the conformal window and becomes chirally symmetric already in the vacuum. Determining $N_f^*$​ has long been a challenge in lattice QCD, as simulations are performed away from the chiral and continuum limits, thus allowing spontaneous symmetry breaking and thermal transitions even for $N_f \ge N_f^*​$. An additional difficulty in the relevant low-temperature region of lattice parameter space is the appearance of an unphysical bulk transition $-$ a discretization artifact that may mask the genuine thermal transition. In this work, we approach the chiral limit by mapping out the phase boundary of the chiral transition in an extended parameter space spanned by the gauge coupling, the number of unimproved staggered fermions, their masses, and the lattice spacing. Our study of the thermal phase transition suggests that, in continuum QCD, the chiral transition is of second order for all $N_f$ up to the onset of the conformal window. At the same time, by mapping out the bulk transition for various $N_f$​ and analyzing its interplay with the thermal transition, we obtain a more refined picture of the general lattice phase structure. Building upon previous studies of many-flavour QCD at $T=0$ and $am=0$, we present an extended lattice phase diagram in terms of $N_t$, $\beta$, $am$, and $N_f$. This understanding of how the conformal window connects to lattice QCD at finite spacing and mass might provide new strategies for inferring the onset of the conformal window from simulations performed away from the chiral and continuum limits.

Speaker: Jan Philipp Klinger (Goethe University Frankfurt)

23 Universal and non-universal finite volume effects in the vicinity of the chiral phase transition in (2+1)-flavor QCD

A quantitative analysis of the universal aspects of QCD phase transition is required to achieve good control of the continuum as well as, infinite volume and chiral limits. In this talk, we will present a careful analysis of the latter two limits, taken at fixed values of lattice cut-off in the framework of (2+1)-flavor QCD. Although this does not yet allow to determine the universality class of the chiral phase transition of QCD, it provides a quantitative analysis of the chiral phase transition that appears in lattice QCD with staggered fermions.
We present results for the renormalized light quark chiral condensate, $M=M_\ell - H\,\chi_\ell$ , where $\chi_\ell$ is the light quark chiral susceptibility, obtained on lattices with temporal extent $N_\tau=8$ and spatial extent $N_\sigma$ varying in the range, $3 N_\tau < N_\sigma<10 N_\tau$ . Light quark masses $m_\ell$ expressed in units of the physical strange quark mass $m_s$ are varied in the range $1/240 \leq m_\ell/m_s \leq 1/27$. We compare results to finite volume scaling functions in the three dimensional O(2) universality class and quantify the contributions of the universal and non-universal parts to the chiral condensate.

Speaker: Sabarnya Mitra (Bielefeld University)

24 QCD phase transition with overlap fermions

We present an update of our lattice study of QCD phase transition with dynamical overlap fermions, which have exact chiral symmetry at finite lattice spacing. We discuss chiral observables and their temperature dependence. Simulations are done in the fixed topological sector and we perform the summation of observables over all topological sectors.

Speaker: Andrey Kotov

25 Investigating Phase Structure of three-flavor QCD with Domain Wall Fermions at Finite Temperature

Phase boundary in the lower left corner of Columbia plot has been studied extensively. We have been tackling this problem using Möbius domain wall fermions of JLQCD type. With an extended analysis as well as the increased statistic around the physical $ud$ quark mass for the three degenerate quarks, we will make conclusion for the $N_t=12$ lattice. With that and glancing the results so far obtained with heavier masses, discussion on the phase structure will be provided.

Speaker: Yasumichi Aoki (RIKEN Center for Computational Science)

26 The QCD Phase Transition at the Physical Point with (2+1)-Flavor Möbius Domain Wall Fermions

We report recent results on the finite-temperature chiral phase transition in (2+1)-flavor QCD with physical quark masses, using the Möbius domain wall fermion (MDWF) action to preserve chiral symmetry to a high precision. Our simulations cover a temperature range from 140 to 250 MeV for two lattice spacings, corresponding to temporal extents of $N_t = 12$ and $16$, with aspect ratios $N_s/N_t$ between 3 and 4. This setup allows us to control for finite-volume and discretization effects. The chiral condensate for domain wall fermions contains ultraviolet-divergent contributions stemming from the finite input quark mass and residual chiral symmetry breaking. We will discuss our method for subtracting these contributions to obtain a renormalized chiral condensate. Our result shows that the disconnected chiral susceptibility develops a pronounced peak whose height does not increase with increasing volume. This suggests that the transition is a smooth crossover rather than first-order. We will report the pseudo-critical temperature and its dependence on the lattice spacing.

Speaker: Yu Zhang (Bielefeld University)

Quantum computing and quantum information

Convener: Apoorva Patel (Indian Institute of Science, Bangalore, India)

27 Hybrid qubit-qumode simulations of QED in 2+1 dimensions

We introduce a novel quantum computational framework for simulating lattice gauge theories by leveraging the advantages of both discrete (qubit) and continuous variables (qumode) quantum computing. The simulations of these hybrid systems can be realized with various quantum hardware platforms like trapped-ion and photonic systems.
By explicitly solving Gauss’s Law at each vertex of the two-dimensional spacial lattice, we construct the QED Hamiltonian for an $N\times N$ plaquette system, retaining only the relevant dynamical degrees of freedom. We then present several hybrid formulations in which the bosonic and fermionic fields are encoded in qumodes and qubits, respectively. To validate our approach, we benchmark the framework by simulating the one-plaquette system - both with and without fermions - and comparing the results to known analytical solutions.

Speaker: Tommaso Rainaldi (Stony Brook University)

28 Quantum simulation of SU(3) lattice gauge theory in the electric basis

I will present an overview and status update of the UIUC high energy and quantum information group's Hamiltonian simulations of SU(3) lattice gauge theory. We have developed and implemented qubit-based simulations of SU(3) gauge theory in the electric basis, in 1,2, and 3 spatial dimensions. I will describe the overall physics strategy, optimization techniques we've designed to control circuit depths, and present simulation results for ground state preparation and observables.

Speaker: Andrew Lytle

29 (2+1)D Wilson Fermions Coupled To $\text{U}(1)$ Background Gauge Fields

Quantum simulation offers a powerful approach to studying quantum field theories, particularly (2+1)D quantum electrodynamics (QED$_3$), which hosts a rich landscape of physical phenomena. A key challenge in lattice formulations is the proper realization of topological phases and the Chern-Simons terms, where fermion discretization plays a crucial role. In this work, we analyze staggered and Wilson fermions (coupled to $\text{U}(1)$ background gauge fields) in the Hamiltonian formulation and demonstrate that staggered fermions fail to induce (2+1)D topological phases, while Wilson fermions admit a variety of topological phases including Chern insulator and quantum spin Hall phases. We additionally uncover a rich phase diagram for the two-flavor Wilson fermion model in the presence of a chemical potential.

Speaker: Emil Otis Rosanowski

30 Toward Quantum Simulation of SU(2) Gauge Theory Using Non-Compact Variables

The orbifold lattice formulation provides a framework for quantum simulation of lattice gauge theories, enabling the explicit and analytical construction of quantum circuits whose computational cost scales polynomially with the number of qubits. This cost can be further reduced by neglecting selected terms and degrees of freedom in the original formulation, leading to two simplified versions. In this talk, we present preliminary lattice Monte Carlo results for SU(2) gauge theory in (2+1) dimensions. Our findings indicate that these simplified orbifold formulations exhibit no issues in reproducing the Kogut–Susskind limit, where the Wilson action is recovered.

Speaker: Emanuele Mendicelli (University of Liverpool (United Kingdom))

31 Quantum computation of Quantum Electrodynamics in higher than one spatial dimension

We present a qubit-based approach for simulating Quantum Electrodynamics (QED), extending the well-established quantum algorithm for scalar field theory to gauge fields. Our method ensures gauge invariance, which automatically enforces Gauss’s law, and is formulated in the lattice framework akin to Wilson or Kogut-Susskind theory. The qubit representation is designed to align with finite Weyl commutation relations, allowing straightforward extension to large representation dimension N, which recovers compact QED in the infinite-N limit. We also study error mitigation strategies; explicit implementations in both 3+1 and 2+1 dimensions have been tested on IBM quantum devices.

Speaker: Bipasha Chakraborty (University of Southampton)

Theoretical developments and applications beyond Standard Model

Convener: Hidenori Fukaya (The University of Osaka)

32 The Axial Charge in Hilbert Space and Their Role in Chiral Gauge Theories

We focus on the fact that the Hamiltonian of the $1+1$D staggered fermion system can be smoothly deformed into that of Wilson fermions. We reinterpret the structure of the axial charge operator proposed by A. Chatterjee, S. D. Pace, and S.-H. Shao using Wilson fermions.
We show that the eigenstates of the axial charge operator can be interpreted as fermion states with a well-defined integer chirality, analogous to those in the continuum theory.
The resulting $1+1$D Hamiltonian formulation is expected to be useful in constructing chiral gauge theories based on the symmetric mass generation (SMG) mechanism. SMG refers to a mechanism by which gapless systems can be gapped without fermion bilinears, purely through appropriate interactions, while preserving symmetries. To demonstrate this, we examine the feasibility of realizing SMG while maintaining the $\mathrm{U}(1)_A$ gauge symmetry generated by the axial charge operator $Q_A$, using the 3-4-5-0 models as examples.

Speaker: Tatsuya Yamaoka (The university of Osaka)

33 Symmetric mass generation and the Nielsen-Ninomiya theorem

The symmetric mass generation (SMG) approach to the construction of lattice

chiral gauge theories attempts to use interactions to render mirror fermions

massive without symmetry breaking, to obtain the desired chiral massless

spectrum. If the zeros that often replace the mirror poles of fermion

two-point functions in an SMG phase are “kinematical” singularities, general

constraints can be formulated on the existence of a chiral fermion spectrum

which are valid in the presence of (non-gauge) interactions of arbitrary

strength, including in any SMG phase. Constructing a one-particle lattice

hamiltonian describing the fermion spectrum, we discuss the conditions for the

applicability of the Nielsen-Ninomiya theorem to this hamiltonian. If these

conditions are satisfied, the massless fermion spectrum must be vector-like.

We comment on the qualitative difference between 4- and 2-dimensional models.

Speaker: Maarten Golterman (San Francisco State University)

34 Lattice chiral gauge theory, U (1) symmetries, and absence of a strong CP problem

It has recently been argued that a proposal to nonperturbatively regulate chiral gauge theories on the boundary of a five-dimensional Euclidian lattice will fail due to the existence of exact U(1) symmetries not present in the target theories. A related observation is that in the presence of gauge fields with nontrivial topology, fermion zeromodes will appear embedded in the extra dimension. We show that for a boundary theory that contains QCD, the exact U (1) symmetry in conjunction with fermion zeromodes in the 5d bulk gives rise to a 4d world with neither a strong CP problem nor a light η′ meson. This solution to the strong CP problem results because the fermion zeromodes in the bulk which quench contributions to the partition function from nontrivial gauge field topology much in the way a massless up quark would, but without altering the hadron spectrum. The consequence is a certain level of nonlocality in the interactions of the η′ meson.

Speaker: Srimoyee Sen

35 A new approach to chiral gauge theory on the lattice

We propose a way to formulate a realistic chiral gauge theory like the standard model on a lattice (or a general simplicial complex in curved spacetime), so that it has the correct continuum limit, with the correct symmetries and (co)homological properties, and no unwanted doublers or anomalies. Building on recent progress by Catterall and collaborators, our approach uses restricted Kahler-Dirac fermions (spinors with a dual interpretation as differential forms).  To obtain the right continuum limit, we find we must appropriately couple the Kahler-Dirac fermions to the tetrad and spin connection one-forms (which describe the geometry of spacetime).  Conceptually, the crucial new point in our formulation is to carefully distinguish between the diffeomorphism group (which is broken by discretization) and the local Lorentz group (which is exactly preserved).  (Joint work with Vatsalya Vaibhav.  Vaibhav's follow-up talk will explain how this picture also suggests a new formulation of gravity on the lattice.)

Speaker: Latham Boyle (Higgs Centre for Theoretical Physics, University of Edinburgh)

36 A Gravitational Theory on the Lattice

This talk will be a follow up of Latham Boyle’s talk on discretizing a chiral gauge theory on the lattice. Building up on the natural geometrical discretization of Kahler-Dirac fermions with different polyforms fields (and the tetrad and spin-connection one forms), we will further see how this geometrical picture also suggests a novel formulation of Einstein gravity on the lattice. We will discuss how this discretization scheme preserves the symmetries and (co)homological properties of the continuum manifold. (Joint work with Latham Boyle.)

Speaker: Vatsalya Vaibhav (University of Edinburgh)

Vacuum structure and confinement

Convener: Ivan Horvath

37 The confining string in 3D U(1) gauge theory beyond effective string theory

The confining string in non-Abelian gauge theories is described to high precision by effective string theory. On the other hand, U(1) gauge theory in three dimensions, while confining, displays some peculiar properties which violate the assumptions of effective string theory. In particular, it is not possible to hold both the mass and string tension fixed in the continuum limit. We report results of high precision numerical simulations of this theory, in particular the ground state energy of closed strings. We show that effective string theory only applies for small bare coupling (far from the continuum). Instead, for large bare coupling (close to the continuum) we find agreement with a very recent theoretical prediction by Aharony, Barel & Sheaffer.

Speaker: Alessandro Mariani

38 Intrinsic width of the flux tube in 2+1 dimensional Yang-Mills theories

We study the profile of the flux tube in non-Abelian gauge theories in the confined phase, by means of precise lattice numerical simulations. We observe a non-Gaussian profile with prominent exponentially decaying tails. From the characteristic decay length length, we extract the intrinsic width of the flux tube. We compute this scale at different values of the temperature in the confined phase.
At low temperature, the profile of the flux tube is well described by the Clem formula, which has been originally proposed in the context of dual superconductivity models. We compare the value of the intrinsic width extracted from fits assuming the Clem formula with the mass gap of the gauge theory and with the critical distance of the Effective String Theory.
At high temperature, on the other hand, it is possible to predict the profile of the flux tube assuming the Svetitsky-Yaffe mapping. We test this prediction against the numerical data, finding a very good agreement, also in the numerical value of the intrinsic width.

Speaker: Lorenzo Verzichelli (Università di Torino, INFN sezione di Torino)

39 Why there is no confinement when vortices proliferate but monopoles do not

Two competing pictures of the confinement mechanism in 3+1D non-abelian gauge theory have been the proliferation of center vortices and the proliferation of magnetic monopoles. In this talk, I will provide a unified and surprising picture of confinement, which clarifies some confusion in the literature concerning the role of vortices. In particular, I will argue that whereas the simultaneous proliferation of vortices and monopoles leads to the gapped confining phase, vortex proliferation without monopole proliferation leads not to confinement but to a gapless Coulomb phase.

Speaker: Mendel Nguyen

40 The simplicity of confinement

I revisit the proposal that colour confinement in non-Abelian gauge theories is related to the dynamics of Abelian magnetic monopoles using methods derived from Topological Data Analysis, which provide a mathematically rigorous characterisation of topological properties of fields defined on a lattice. After introducing homology, I shall discuss how this concept can be used to quantitatively analyse the behaviour of Abelian monopoles identified through the Maximal Abelian Projection across the deconfinement phase transition of SU(3) Yang-Mills. Specifically, I define an observable called “simplicity”, which measures the number of topologically non-trivial loops per connected component in a current network. A finite-size scaling of the ensemble-averaged simplicity of Abelian magnetic monopole currents provides the expected value of the critical coupling with an accuracy that is generally higher than that obtained with conventional thermodynamic approaches at comparable statistics. Initial results for QCD will also be discussed.

Speaker: Biagio Lucini (Queen Mary University of London (UK))

41 The mass of the Baryon Junction in $(2+1)d$

We present a systematic study of baryonic flux tubes in $\mathrm{SU}(3)$ Yang--Mills theory in $(2\!+\!1)$ dimensions. A recent next-to-leading–order derivation within the Effective String Theory framework has, for the first time, made explicit the corrections proportional to the baryon--junction mass $M$, up to order $1/R^2$ (where $R$ is the length of the confining strings), opening the possibility of its non-perturbative determination. One of the main goals of this paper is, through high-precision simulations of the three-point Polyakov-loop correlator, to measure for the first time the baryon–junction mass. By isolating the predicted $1/R^{2}$ term in the open-string channel, we obtain the value $\frac{M}{\sqrt{\sigma}} = 0.1355(36) $, similar to the phenomenological value which is used
to describe a hadron. In addition, studying the high temperature behaviour of the baryon, we present a new test of the Svetitsky--Yaffe conjecture for the $\mathrm{SU}(3)$ theory in three dimensions. Focusing on the high-temperature regime just below the deconfinement transition, we compare our lattice results for Polyakov-loop correlators with the quantitative predictions obtained by applying conformal perturbation theory to the three-state Potts model in two dimensions, and find excellent agreement.

Speaker: Dario Panfalone

16:10 Coffee break

Algorithms and artificial intelligence

Convener: Lorenzo Barca (DESY)

42 A scalable flow-based approach to mitigate topological freezing

In recent years, flow-based samplers have emerged as a promising alternative to traditional sampling methods in lattice gauge theory. In this talk, we will introduce a class of flow-based samplers known as Stochastic Normalizing Flows (SNFs), which combine neural networks with non-equilibrium Monte Carlo algorithms. We will show that SNFs exhibit excellent scaling with the volume in lattice SU$(3)$ gauge theory. Then, we will present an application to SU$(3)$ gauge theory with open boundary conditions, demonstrating how this approach represents an efficient strategy for the sampling of topological observables at fine lattice spacings.

Speaker: Elia Cellini (University of Edinburgh)

43 Multilevel Normalizing Flow Samplers with Built-in Variance Reduction in LFT

Abstract:
We present a multilevel generative sampler for lattice field theories that combines local upsampling with normalizing flows (NFs). At each level, new sites are first sampled independently from Gaussian mixture models and then refined with NFs to introduce correlations, while the coarse sites remain embedded in the finer lattice. Our results show that hierarchical generative sampling scales more efficiently than training single-level models directly at large lattice sizes. We further introduce a multilevel estimator that prioritizes sampling at the coarser scales, yielding significant variance reduction.

Speaker: Ankur Singha (Technical University Berlin)

44 Monte Carlo estimates of flow fields for sampling and noise problems

Learned field transformations may help address ubiquitous critical slowing down and signal-to-noise problems in lattice field theory. This approach has close ties to trivializing maps and numerical stochastic perturbation theory, in which field transformations are defined by integrating flow fields that exactly solve a local transport problem. In this talk, I will discuss a new Monte Carlo approach to estimating these flow fields, which can then be used directly in such contexts or as a means of generating "ground truth" data for machine learning approaches.

Speaker: Gurtej Kanwar (University of Edinburgh)

45 A novel gauge-equivariant neural network architecture for preconditioners in lattice QCD

The main contribution to the cost of Lattice QCD calculations typically comes from solving the Dirac equation. Using preconditioners such as multigrid, this computational cost can be reduced significantly. We introduce a novel gauge-equivariant neural network architecture for preconditioning the Dirac equation. We study the behavior of this preconditioner as a function of topological charge and lattice volume and compare the results to multigrid. We also discuss the setup cost of multigrid and our architecture to give a fair comparison between the two.

Speaker: Simon Pfahler (University of Regensburg)

46 Robustness and over-parameterization

In many modern machine learning applications, models are often trained
to near zero "training loss" (in other words, to interpolate the
training data), while also having far more training parameters than the
"number of data points". This appears to violate traditional
rules-of-thumb for avoiding overfitting, and considerable work has thus
been devoted to gain a better understanding of such
over-parameterization. A more recent development is an interesting
direction suggested by Bubeck and Sellke, who postulated that, in
certain settings, a much larger number of parameters may indeed be
required to interpolate the training data if the model being trained is
also required to be "robust": small modifications to the model input
should not lead to very large changes in the model output.

In this talk, we will survey this formulation of the connections between
robustness and over-parameterization. We will also present the
conceptual view that a bias-variance type decomposition for the loss
function lies at the heart of the results of Bubeck and Sellke, and then
use this idea to show that the setting of losses corresponding to
Bregman divergences is the natural setting for understanding the
connection between robustness and over-parameterization in this formulation.

Speaker: Piyush Srivastava (Tata Institute of Fundamental Research)

Hadronic and nuclear spectrum and interactions

Convener: Maxim Mai (University of Bern)

47 Charm tetraquarks investigation using CLS lattices

I will summarize various lattice investigations of charmed and charmonium tetraquarks using CLS lattice QCD ensembles that we have performed in the past one year.

Speaker: M. Padmanath (The Institute of Mathematical Sciences Chennai)

48 Lattice study of ccus tetraquark channel in D(*)Ds(*) scattering

In this work, we investigate the possible existence of a strange partner of the $T_{cc}$ tetraquark with flavor content $cc\bar{u}\bar{s}$ using lattice QCD. We determine the coupled-channel $DD_s^* - D^*D_s$ scattering amplitudes in the axialvector ($J^P = 1^+$) channel, as well as the elastic $DD_s$ scattering amplitude in the scalar ($J^P = 0^+$) channel. The calculations are performed on two ensembles from the CLS consortium with $m_{\pi} \approx 280\,\text{MeV}$, lattice spacing $a \approx 0.09\,\text{fm}$, and spatial extents $L/a = 24$ and $32$. The two-meson spectrum in the finite volume is determined for the $DD_s$, $DD_s^*$, $D^*D_s$, and $D^*D_s^*$ channels. This is achieved through a variational analysis of two-point correlation matrices constructed using a large basis of bilocal two-meson operators within the distillation framework. To extract the infinite-volume amplitudes, we employ Lüscher’s formalism as well as a Lippmann-Schwinger equation based quantization condition in a plane-wave basis. Despite the presence of nontrivial interactions in both channels, no non-spurious pole singularities are found in the S-wave amplitudes within the constrained energy region.

Speaker: Tanishk Shrimal (The Institute of Mathematical Sciences)

49 Importance of local tetraquark operators for the $T_{cc}(3875)^+$ spectrum

The doubly charmed tetraquark $T_{cc}(3875)^+$ observed at LHCb has attracted considerable interest in recent years. To accurately determine its finite-volume spectrum, a variational analysis using a large basis of operators, including bilocal scattering operators but also local tetraquark operators, should be used. Using Wilson-clover fermions at the $SU(3)$-flavour-symmetric point, we investigated the importance of local tetraquark operators for the $T_{cc}$ spectrum by adding them to a large basis of bilocal $DD^*$ and $D^*D^*$ scattering operators. We performed this calculation using the distillation framework combined with a position-space sampling method [arXiv:2412.09246]. Upon including the local tetraquark operators, we observe a relatively small shift in the ground state energy, whereas the first excited state shifts significantly. Finally, I will show the effect on the $s$-wave scattering phase shift obtained from a Lüscher analysis.

Speaker: Andres Stump (Humboldt-Universität zu Berlin)

50 $T_{cc}$ pole trajectory

The recent discovery of $T_{cc}$ has attracted several lattice QCD
as well as other studies of $T_{cc}$ pole. Though for $T_{bb}$ there
is a consensus about the existence of a deeply bound state, no such
consensus have been reached for $T_{cc}$. On top of that the discovery
of Left Hand Cut made the pole analysis using Lüscher’s method
difficult. In this situation it is desirable to study the pole
trajectory of $T_{cc}$ by varying the heavy and light quark masses.
We performed such a study of $T_{cc}$ pole trajectory on $N_f=2+1+1$
HISQ ensembles.

Speaker: Protick Mohanta (The Institute of Mathematical Sciences, Chennai, Tamil Nadu 600113)

51 Lattice QCD Investigation of Doubly Bottom and Bottom-Strange Tetraquarks in the Isoscalar Channel

We present our recent investigation on doubly bottom and bottom-strange tetraquarks in the isoscalar channel in search of a possible tetraquark bound state. The calculations are performed on four ensembles with dynamical quark fields up to the charm quark generated by the MILC Collaboration with various lattice spacings. Multiple volumes have been used to account for finite volume effects. Overlap action has been used to calculate light and strange quark propagators. Finite volume energy has been calculated using the variational method followed by rigorous scattering amplitude analysis calculation $\it{à ~la}$ Lüscher. We find strong evidence for a deeply bound state in the doubly bottom tetraquark channel, but no conclusive evidence for the existence of a bottom–strange tetraquark.

Speaker: Bhabani Sankar Tripathy (The Institute of Mathematical Sciences, Chennai)

Hadronic contribution to the magnetic moment of muon

Convener: Marina Krstic Marinkovic (ETH Zurich)

52 HLbL contribution to the muon g-2 using twisted-mass fermions at the physical point

We present updated results for the hadronic light-by-light (HLbL) contribution to the muon anomalous magnetic moment. The calculations are based on ETMC's $N_f = 2+1+1$ Wilson-clover twisted-mass ensembles at the physical point. We perform continuum extrapolations for the strange- and charm-quark connected contributions, and report on our results for the light-quark connected and light-light (2+2) disconnected contributions at one lattice spacing.

Speaker: Nikolaos Kalntis (University of Bern)

53 Toward sub-percent precision in muon g-2

We present a progress update on the Fermilab Lattice, HPQCD, and MILC collaboration's ongoing effort to compute the hadronic vacuum polarization (HVP) contribution to the muon g-2. In particular, we describe the current status for the dominant isospin-symmetric leading order HVP quantities, namely the connected light-, strange-, and charm-quark contributions, including new data on our finest lattice spacing to date, 0.04 fm, where the one-link vector current has now been added for strange and charm, as well as for the light quarks. Preliminary results for the long-distance disconnected and I=0 contributions are also discussed. Finally, progress toward a complete (NLO) determination of the HVP contribution is outlined. All calculations are performed on 2+1+1 flavor HISQ ensembles with a physical pion mass. A companion talk will discuss the status of corresponding isospin-breaking corrections.

Speaker: Shaun Lahert

54 Toward sub-percent precision in muon $g-2$: Isospin breaking corrections to HVP

An ongoing project of the Fermilab Lattice, HPQCD, and MILC collaborations is the precision calculation of the hadronic vacuum polarization (HVP) contribution to the anomalous magnetic moment of the muon. In this talk, we present the isospin breaking corrections to the connected and disconnected contributions to HVP with a focus on the dominant, long-distance contributions to these correction. Results for both strong isospin breaking and QED are discussed. All calculations are performed on $N_f=2+1+1$ highly-improved staggered-quark (HISQ) ensembles with physical pion masses. A companion talk will discuss the status of the isospin-symmetric contributions.

Speaker: Jacob Sitison (University of Colorado Boulder)

55 Factorizing the position space photon propagator for electromagnetic corrections to $(g-2)_\mu$

Electromagnetic corrections to n-point functions on the lattice can be calculated by using a position space photon propagator. In this representation the propagator depends on the difference between the two vertices connected by the internal photon, leading to a volume square sum. The sum can be avoided by fixing one of the vertices to a single point with the downside of drastically reducing the sampling of the vertex. We explore various ways of factorizing the position space photon propagator, which disentangles the dependence on the difference. It allows the sum over all lattice sites for the two vertices connected by the internal photon.

We compare the point-source implementation with two methods, where the propagator is factorized, by calculating the isospin violating part of the hadronic vacuum polarization of $(g-2)_\mu$. The calculations are performed on a single CLS ensemble, N451, with a pion mass of 286 MeV.

Speaker: Dominik Erb

56 ETMC results on the hadronic vacuum polarization contribution to the muon g-2 in isospin symmetric QCD

We present results by ETMC on the leading-order hadronic vacuum polarisation (LO-HVP) contribution to the muon anomalous magnetic moment within isospin symmetric $N_f=2+1+1$ QCD. In our computation, we use Wilson–clover twisted-mass quarks in a sequence of simulations at large volumes, realistic pion masses, four lattice spacings and two different valence-quark regularisations for the dominating quark-connected terms.

Speaker: Antonio Evangelista (University and INFN of Rome Tor Vergata)

QCD at nonzero temperature and density

57 Complex Langevin simulations with a kernel

Lattice simulations based on importance sampling suffer from the infamous sign problem when applied to certain physical systems of interest, such as QCD at finite baryon density or real-time quantum field theories. A possible way out is provided by the complex Langevin approach, which is based on a stochastic evolution of complexified degrees of freedom in an auxiliary time direction. However, complex Langevin simulations sometimes fail to produce correct results despite apparently converging correctly. In this talk, I will discuss possible reasons of failure and, in particular, how they may be mitigated by the introduction of a so-called kernel into the complex Langevin equation. Apart from applying such kernels to different systems, I will also outline a novel condition for correctness of the complex Langevin approach.

Speaker: Michael Mandl (University of Graz)

58 Finite density lattice QCD as an inverse problem (aka analytical continuation from imaginary to real chemical potential via Cauchy integral formula)

Given the sign problem, many simulations of finite density lattice QCD are performed at imaginary values of the baryonic chemical potential. One is thus left with the problem of analytically continuing results to (physical) real values. We have recently introduced a new method to perform this analytical continuation, based on the Cauchy integral formula, starting from which we define and solve an inverse problem. It turns out that the method can be successfully implemented, as we show in the case of the computation of the number density. As a check, we show that results for derivatives of the number density (i.e. higher order moments) can be obtained, fully consistent with the values available in the literature. The method, as we will show, is more general than it appears in this context, having something to say about many other relevant inverse problems.

Speaker: Francesco Di Renzo

59 Developments on analytic continuation from imaginary chemical potential

Computations at imaginary values of chemical potential is one of the most popular ways to tackle the sign problem in lattice simulations.
For this reason, it is important to study different ways to perform the analytic continuation to the real axis.
In the context of the Bielefeld-Parma collaboration, we have been generating data which fed our multi-point Padé analysis of the QCD phase diagram.
We report on our studies on different techniques to perform the analytic continuation comparing the different systematic effects.
In particular, we will compare results coming from a method based on Cauchy integral formula with what we get from more traditional methods, including the analytic continuation of multi-point Padé approximants.

Speaker: Marco Aliberti (University of Parma and INFN)

60 QCD phase boundary from strangeness fluctuations on a high statistics lattice data set

Mapping the QCD phase structure at finite baryon density remains a challenging problem because direct simulations are hindered by the sign problem. By analyzing results at vanishing and purely imaginary chemical potentials, we identified strangeness susceptibility, in the case of strangeness neutrality, as a proxy for the chiral transition. We exploit this observation to investigate the QCD transition line at large baryon chemical potentials up to $550$ MeV, thanks to a Taylor expansion up to NNNNLO based on extreme-statistics runs on a $16^3 \times 8$ lattice. We also investigate the non-strangeness neutral scenario, and discuss possible implications for the existence of a critical point.

Speaker: Piyush Kumar (Bergische Universität Wuppertal)

61 An accurate description of 2+1 flavour QCD in a low-energy EFT

We build an EFT which accurately captures low energy physics of the chiral sector of QCD. When fitted to properties of pions at finite temperature obtained from lattice simulations of 2+1 flavour QCD, it accurately reproduces the crossover temperature seen in the simulations. Its predictions for other quantities are shown. The EFT can then be used for analytic continuation to real time. An interesting property of the continuation is demonstrated.

Speaker: Sourendu Gupta (Tata Institute of Fundamental Research)

Quantum computing and quantum information

Convener: Emilie Huffman (Wake Forest University)

62 Spectrum Generating Algebra in Higher Dimensional Gauge Theories

The existence of an approximate spectrum-generating algebra in the PXP model has been extensively studied as a mechanism underlying quantum many-body scars. Since the PXP model can be mapped to a gauge theory in one spatial dimension, a natural question arises: can similar algebraic structures and scar-like dynamics occur in higher-dimensional gauge theories? In this work, we show that this is the case by analyzing different types of quantum revivals in higher-dimensional gauge theories. Furthermore, we outline a pathway toward their experimental realization, as a new direction for exploring non-ergodic dynamics in constrained quantum systems.

Speaker: Joao C. Pinto Barros (Institute for Theoretical Physics, ETH Zurich)

63 Hilbert Space Fragmentation and Gauge Symmetry

Lattice Hamiltonians with gauge symmetry are characterized by a local symmetry transformation per lattice site and may even exhibit further higher-form symmetries. There are then an exponentially large number of dynamically disconnected symmetry sectors, most of which are not translation-invariant. This results in localized dynamics even without the presence of disorder. An exponential number of dynamically disconnected sectors can also occur in systems that have no such symmetries, and this unexplained phenomenon is known as fragmentation. In this talk, I will discuss the parallels between the dynamics of systems with gauge symmetry and those that are fragmented. Additionally, I will discuss an emergent gauge symmetry, which is valid in a subset of sectors of the $S=1$ dipole-conserving spin chain, in an attempt to explain this model's fragmentation.

Speaker: Thea Budde (ETH Zürich)

64 Parton distribution function in 1+1D Schwinger Model using Quantum Computing

We present a lattice calculation of the parton distribution function (PDF) of the lightest positronium system employing the 1+1D Schwinger model in the Hamiltonian formulation, implemented within a quantum computational framework on an IBM quantum computer. Our setup employs a total of 11 qubits: 10 qubits represent stagger fermions sites, which correspond to five spatial lattice sites and one ancillary qubit for determination of matrix element of a bilinear operator via Hadamad test. The PDF is obtained as the Fourier transform of this bilinear operator, which is measured along the light-cone direction. This approach offers a key advantage over traditional Euclidean lattice calculations, which require various approximations such as the LaMET framework. Compared with classical methods, quantum computation offers the advantage of not being limited in the accessible range of parton momentum fraction $x$ due to renormalon ambiguity particularly at $x=0$ and $x=1$, and the difficulty of accessing non-valence partons. A PDF calculation with 3+1 dimensional QCD near $x=0$ or $x=1$ will be a clear demonstration of the quantum advantage on a problem with great scientific impact. The real quantum computer and simulator results match well within the estimated statistical error, although the error remains sizable. Our study demonstrates that meaningful PDF extraction is feasible on current quantum devices by reducing the two-qubit gate depth from 5000 to 500. Future generations of quantum hardware will be capable of maintaining greater circuit depth and hold promise for achieving precise PDF calculations.

Speaker: Ghanashyam Meher (National Taiwan University)

65 Measurement-Induced Entanglement Dynamics in a Z₂ Lattice Gauge Theory

Quantum simulations of fundamental gauge theories require a thorough understanding of non-unitary dynamics that arise from interactions with an environment, including measurements. This talk focuses on the one-dimensional Z₂ gauge theory, a foundational model for probing such effects. Using tensor network calculations, we investigate the dynamics of entanglement entropy when physical observables are measured at varying rates. We further demonstrate that the interplay between unitary evolution and projective measurements gives rise to distinct behaviours in the weak and strong coupling regimes. Specifically, we show that for a fixed measurement rate, the late-time entanglement entropy saturates to different, characteristic values in each regime. These findings reveal signatures of measurement-induced effects and provide crucial insights for benchmarking and interpreting results from near-term quantum simulators.

Speaker: Dr Nisa Ara (Tata Institute of Fundamental Research, Mumbai)

Standard Model parameters

Convener: V. Ravindran

66 Strong coupling constant from the static energy

The strong coupling constant $\alpha_s$ can be obtained from the static energy. For short distances, the static energy can be calculated both on the lattice, with the use of Wilson line correlators, and with the perturbation theory up to three loop accuracy with leading ultrasoft log resummation. Comparing lattice data with the perturbative expression allows for a precise measurement of the $\alpha_s$. In this talk, we will update the TUMQCD 2+1-flavor $\alpha_s$-extraction and report on the progress with the 2+1+1 extraction.

Speaker: Viljami Leino

67 Towards determination of the strong coupling alpha_s(m_Z) from four flavor lattice QCD using the continuous beta-function method

Precise determination of the strong coupling, $\alpha_s$, at the electroweak scale $m_Z$ is crucial for high-energy phenomenology and precision QCD tests. We apply the continuous $\beta$-function method to four-flavor lattice QCD with highly improved staggered quarks. This approach defines the coupling via gradient flow and allows direct determination of the $\beta$-function in the infinite volume continuum limit. I will present the status of this program, focusing on the analysis pipeline and systematic tests. We examine our control over the chiral, infinite-volume, and continuum limits for the high-precision determination of $\alpha_s(m_Z)$.

Speaker: Yash Mandlecha (Graduate Research Assistant)

68 Determination of the SU(3) Yang-Mills running coupling

The decoupling strategy allows to obtain the value of the strong coupling in QCD from the running in pure gauge. Here we present our strategy to determine the running in the SU(3) Yang-Mills theory. We use a finite volume scheme with twisted boundary conditions and a step-scaling approach based on a gradient flow coupling. We show preliminary results for the continuum extrapolation of the step- scaling function. Compared with other finite volume approaches, we expect a reduced statistical error due to the translational invariance of the boundary conditions, and a smooth approach to the continuum limit without linear cutoff effects, thanks to an improved setup with good scaling properties.

Speaker: Isabella Leone Zimmel

Theoretical developments and applications beyond Standard Model

Convener: Fabian Zierler (Swansea University)

69 Impact of SUSY on the dynamical emergence of the spacetime in the type IIB matrix model with the Lorentz symmetry "gauge fixed"

The type IIB matrix model has been proposed as a non-perturbative formulation of string theory. Its partition function is divergent due to the non-compactness of the Lorentz group. This has led to a new definition of the type IIB matrix model with the Lorentz symmetry fixed by the Faddeev-Popov procedure in a non-perturbative manner. We study this model using the complex Langevin method, and discuss the impact of supersymmetry on the dynamical generation of the (3+1)-dimensional spacetime.

Speaker: Takehiro Azuma (Setsunan University)

lattice251103_azuma.pdf

lattice251103_azuma.ppt

70 Lattice Studies of Two-Dimensional Maximally Supersymmetric Yang–Mills Theory for Tests of Gauge-Gravity Duality

We present our ongoing work on two-dimensional maximally supersymmetric Yang–Mills (2D MSYM) theory using lattice techniques. The continuum theory is obtained from the dimensional reduction of four-dimensional N = 4 supersymmetric Yang–Mills theory. We construct both the continuum and lattice versions of the 2D MSYM theory. The lattice action preserves a subset of supersymmetries. We extend the existing lattice codes with new routines to accommodate the additional terms in the lower-dimensional theory. This lattice construction enables us to perform Rational Hybrid Monte Carlo simulations of 2D MSYM and facilitates the exploration of its continuum limit. Our work contributes to the numerical study of maximally supersymmetric gauge theories and supports the ongoing efforts to test gauge-gravity duality and investigate related non-perturbative phenomena.

Speaker: BANA SINGH

71 Dark pion scattering and vector resonance in Sp(4) gauge theory

We perform non-perturbative lattice studies of pseudoscalar particle scattering states and of the vector resonance state in Sp(4) gauge theory coupled to two fundamental Dirac fermions. In the context of dark matter phenomenology, the corresponding continuum theory can provide a production mechanism for strongly interacting massive particles that serve as a candidate for dark matter. We compute the finite-volume spectrum of the composite states interpolated by both vector and two-pseudoscalar operators, and employ Luscher's formula to extract the information concerning properties of the infinite-volume scattering processes in the 10-plets of the unbroken Sp(4) group, corresponding to the isospin-1 channel of two-flavour QCD. We present our preliminary findings for the cases with large, moderate, and relatively small fermion masses.

Speaker: JONG-WAN LEE (IBS-CTPU)

72 The axion-photon coupling from lattice QCD

The QCD axion is one of the most promising solutions to the strong CP problem, as it is also a viable dark matter candidate. Moreover, a large fraction of the current experimental searches focus on its coupling to photons. In this talk, we present the first determination of the QCD corrections to the model-independent part of the axion–photon coupling from a first-principles lattice QCD calculation. The continuum limit is taken with two independent methods to ensure the robustness of the result. Using our result for the coupling, we update the current theoretical and experimental bounds in the coupling-mass plane.

Speaker: José Javier Hernández Hernández (University of Bielefeld)

73 Holography on the lattice: Evidence from 3D supersymmetric Yang--Mills theory

We present new results from our lattice investigations of maximally supersymmetric Yang--Mills theory in three dimensions, focusing on its nonperturbative phase diagram. Using a lattice formulation that preserves part of the supersymmetry algebra at finite lattice spacing, we study the spatial deconfinement transition, which holography relates to the transition between localized and homogeneous black branes in the dual gravity theory. Our analysis employs $N_L^2 \times 8$ lattices with $N = 8$ colors in the SU($N$) gauge group, considering four aspect ratios $\alpha = N_L / N_T \leq 4$ with $N_L = 16, 20, 24,$ and $32$. The resulting transition temperatures are consistent with the holographic low-temperature, large-$N$ prediction $T_c \propto \alpha^3$, providing further evidence for the gauge-gravity correspondence in this setting.

Speaker: Anosh Joseph (University of the Witwatersrand)

Tuesday 4 November

Plenary session

Convener: Sourendu Gupta (Tata Institute of Fundamental Research)

74 Lattice QCD at finite temperature and density

I will review the status of lattice QCD in extreme conditions—finite temperature, nonzero baryon chemical potential, and strong magnetic fields. Emphasis will be on the QCD phase structure and bulk thermodyanmics.

Speaker: Heng-Tong Ding

75 Experiment and Lattice: Understanding High-Temperature QCD Matter

We will survey how RHIC and LHC measurements constrain the properties of QCD matter when interpreted with lattice-QCD inputs. The talk will: (i) present hydrodynamic descriptions of momentum and angular distributions using a lattice-anchored equation of state at μB≈0 and its finite-density extensions relevant to the RHIC Beam Energy Scan; (ii) confront fluctuation measurements with lattice conserved-charge susceptibilities to illuminate QCD thermodynamics and search for a possible critical point; and (iii) show data-driven extractions of transport coefficients—η/s(T), ζ/s(T), and heavy-quark diffusion Ds(T)—where lattice priors reduce model degeneracy. During the course of the talk we will highlight the interdependencies between heavy-ion experiment and lattice calculations, and close with some opportunities for deeper experiment–lattice synergy in the EIC era.

Speaker: Bedangadas Mohanty (National Institute of Science Education and Research (NISER) (IN))

11:00 Coffee break

Plenary session

Convener: Rajiv V Gavai (UM-DAE CEBS, Mumbai)

76 Spectral Properties of the Quark-Gluon Plasma from Lattice QCD

Dynamical probes such as thermal photons and quarkonia provide valuable insight into the properties of the quark-gluon plasma (QGP) created in heavy-ion collisions. The relevant information is encoded in their spectral functions. Extracting these spectral functions from lattice correlators is a challenging task due to the ill-posed nature of the inverse problem, which requires additional physics input. In this talk, I will present recent lattice results on the spectral functions of some dynamical probes related to the thermal photon rate, quarkonia, and heavy-quark diffusion coefficients.

Speaker: Dibyendu Bala (Bielefeld University)

77 Non-perturbative QCD thermodynamics with Nf=3 up to the electroweak scale

Studying the behavior of QCD at high temperatures is essential for understanding the properties of strongly interacting matter and its role in the evolution of the early Universe. A key quantity in this context is the QCD Equation of State. I present a non-perturbative determination with three massless quark flavors, covering a wide range of temperatures, from the electroweak scale down to 3 GeV, and smoothly connecting to the low-temperature regime. The comparison with perturbative predictions shows that, even at temperatures approaching the electroweak scale, the Equation of State can be reproduced only when adding higher-order terms in the strong coupling expansion, including non-perturbative contributions.
The strategy that allows the investigation of QCD in this previously unexplored high-temperature regime combines shifted boundary conditions with a definition of the lines of constant physics based on the running of a non-perturbatively defined renormalized coupling. This methodology is general and can be applied to QCD with four or five massive quark flavors.

Speaker: Michele Pepe (INFN - National Institute for Nuclear Physics)

78 ILDG

Speaker: Christian Schmidt-Sonntag

79 LAVA

Speaker: Simon Hands (University of Liverpool)

13:00 Lunch break [Followed by LDIC Meeting]

Algorithms and artificial intelligence

Convener: Simran Singh (HISKP, University of Bonn)

80 A Machine Learning Approach for Lattice Gauge Fixing

Gauge fixing is an essential step in lattice QCD calculations, particularly when studying gauge-dependent observables. Traditional iterative algorithms for gauge fixing are computationally expensive and often suffer from critical slowing down near fixed points, as well as scaling bottlenecks on large lattices. We present a novel machine learning framework for lattice gauge fixing, in which Wilson lines are utilised to construct gauge transformation matrices. The training parameters of the model are optimised via gradients obtained from backpropagation of a convolutional neural network. Preliminary tests on SU(3) gauge ensembles demonstrate the potential of this approach to improve the efficiency of lattice gauge fixing.

Speaker: Ho Hsiao (Center for Computational Sciences, University of Tsukuba)

81 Machine Learning-Based Estimation of Cumulants of Chiral Condensate via Multi-Ensemble Reweighting with Deborah.jl

Investigating the critical endpoint of the finite-temperature QCD phase transition requires higher-order cumulants of the chiral condensate. These, in turn, involve traces of inverse Dirac operator powers $\text{Tr}\,M^{-n}$ ($n=1,2,3,4$). Because direct computation with the Conjugate Gradient method is computationally expensive, we adopted a machine-learning strategy using gradient-boosted decision tree regression with bias correction [1], trained on data from simulations with the Iwasaki gauge action and Wilson clover fermion action [2]. The labeled set was split into training and bias-correction subsets, and the trained model was applied to unlabeled data, with the resulting bias-corrected ML estimates then examined. Building on earlier progress [3], we further applied multi-ensemble reweighting and interpolation to estimate cumulants at the first-order phase transition point, investigating dependence on the fraction of labeled and training data. Using $\text{Tr}\,M^{-1}$ from original measurements both as a direct component of the cumulant calculation and as an input feature for training ML models to estimate $\text{Tr}\,M^{-n}$ ($n=2,3,4$), we found that even with only 1% labeled data, susceptibility, skewness, and kurtosis agreed almost perfectly with the original, suggesting that the computational cost can be reduced to approximately 25.8% of the original. To further probe avenues for reducing computational cost, we also incorporated the Plaquette and Rectangle loops as input features. Using these, we performed bias-corrected ML estimation for all four $\text{Tr}\,M^{-n}$ in a single workflow and then carried out multi-ensemble reweighting. Unlike our main methodology, where original $\text{Tr}\,M^{-1}$ is directly used and its statistical fluctuations naturally propagate through the analysis, this setup relies solely on correlations between the features and target. This also allowed us to investigate, in detail, the sensitivity of cumulant estimates to the presence or absence of bias correction.

[1] B. Yoon et al., Phys. Rev. D 100, 014504 (2019), arXiv:1807.05971 [hep-lat].
[2] H. Ohno et al., PoS LATTICE2018, 174 (2018), arXiv:1812.01318 [hep-lat].
[3] B. J. Choi et al., PoS LATTICE2024, 033 (2024), arXiv:2411.18170 [hep-lat].

Speaker: Benjamin Jaedon Choi (Center for Computational Sciences, University of Tsukuba)

82 Parameter Optimization of Domain-Wall Fermion using Machine Learning

Domain-wall fermions provide a good lattice realization of chiral fermions by introducing an additional fifth dimension. Achieving improved chiral symmetry typically necessitates increasing the extent of this dimension at the expense of significantly higher computational cost. We propose a machine-learning-based parameter-optimization approach that emulates the effect of a longer fifth dimension while keeping it short, thereby reducing the computational cost.

Speaker: Shunsuke Yasunaga (Institute of Science Tokyo)

83 Investigating the Hybrid Monte Carlo with coherent conjugate momenta

In this talk, we discuss tests of the Hybrid Monte Carlo algorithm using four dimensional pure SU(3) gauge theory when the conjugate momenta are not chosen as random Gaussian variables of uniform variance for each lattice site, but instead are represented as different normal modes across the lattice volume, with variable variance. Generically, this involves simulating in a fixed gauge. One goal of this work is to investigate whether appropriate conjugate momentum modes can, for example, speed up a particular part of the evolution of the lattices, such as topological charge.

Speaker: Robert Mawhinney (Columbia University)

Hadronic and nuclear spectrum and interactions

Convener: Felix Benjamin Erben

84 Nucleon to Delta(1232) Resonance Transition Form Factors from Lattice QCD

We present progress in a lattice QCD study of the electromagnetic and axial $N\to\Delta(1232)$ resonance transition form factors. Our long-term aim is to apply the Lellouch-Lüscher formalism to extract infinite-volume $N\to N\pi$ form factors from finite-volume matrix elements. We previously computed the required $N\pi$ scattering amplitudes on an ensemble with $N_f=2+1$ clover fermions at $m_\pi \approx 255$ MeV and $L\approx2.8\,\rm{fm}$, and obtained the $\Delta$ resonance parameters $m_\Delta= 1378(11)\,\rm{MeV}$ and $g_{\Delta-N\pi} = 23.8(2.8)$. We have now additionally computed the three-point functionsfor six source-sink separations ranging from $t_{\rm sep}=0.7 - 1.2\,\rm{fm}$. Here, we present a first look at the three-point functions data by extracting the $N\to\Delta$ transition form factors using the single-hadron approach.

Speaker: Srijit Paul

85 Towards the time-like pion form factor beyond the elastic regime using domain-wall QCD

In this work we investigate the time-like pion form factor from lattice QCD, a quantity interesting for its physics content and its phenomenological reach. This observable can be calculated in the elastic region using the finite-volume approach, up to the first (four-particle) open channel. With the goal of accessing the exclusive two-pion form factor in the inelastic region, starting from a three-point correlator involving the vector current and two (temporally-displaced) pion interpolating operators, we examine the associated underlying spectral density and relate it to the form factor using recent developments based on inverse-problem techniques. The status of our preliminary calculation performed on RBC/UKQCD ensembles using domain-wall fermions is presented.

Speaker: Gabriele Morandi (Università degli Studi di Milano - Bicocca)

86 Two-pion scattering amplitude from Lattice QCD using staggered fermions

Scattering processes featuring the strong interactions can be studied using lattice QCD by means of the Lüscher formalism. This approach relies on analyticity and unitarity of the $S$-matrix to relate infinite-volume scattering amplitudes to finite-volume energy levels. However, lattice QCD simulations employing rooted staggered fermions manifest unitarity violation as an $\mathcal{O}(a^2)$ lattice artifact. Moreover, the meson sector of this theory contains multiple pions as a result of taste-splitting effects. These features restrict the applicability of the Lüscher formalism on observables computed using staggered fermions. Backed by calculations in the corresponding effective theory--Staggered Chiral Perturbation Theory--in this work, we discuss possible approaches to deal with the challenges of extracting scattering amplitudes from lattice QCD with staggered quarks. In particular, we focus on the simpler case of pion-pion scattering in the isospin-2 channel, and discuss prospects for other channels.

Speaker: Adeilton Dean Marques Valois

Hadronic contribution to the magnetic moment of muon

Convener: Christoph Lehner (University of Regensburg)

87 The three-loop hadronic vacuum polarization in chiral perturbation theory

Hadronic vacuum polarization is a key observable in low-energy QCD, and is famously the greatest contributor to theoretical uncertainty in the muon magnetic moment. Its long-distance part in particular is a weak point of the current best lattice QCD computations. We compute it to next-to-next-to-next-to-leading order in chiral perturbaion theory, capturing the lowest-energy hadronic contributions to unprecendentd precision and opening the door for improved control over lattice finite volume effects. The result depends on a small number of low-energy constants, whose values are under control. This calculation pushes the envelope of high-order chiral perturbation theory and of the evaluation of multiloop integrals with massive propagators, thereby extending the toolbox for precision calculations in very low-energy QCD.

Speaker: Mattias Sjö (CPT Marseille)

88 Hadronic contributions to $\alpha(Q^2)$ and $\sin^2\theta_W(Q^2)$ from spectral reconstruction on the lattice.

We present progress towards a new determination of the hadronic vacuum polarization (HVP) function $\Pi(Q^2)$ relevant for the running of the electromagnetic coupling and the electroweak mixing angle. In the conventional time–momentum representation, strong correlations induced by the kernel prevent reliable continuum extrapolations. To address this issue, we reconstruct smeared spectral densities from Euclidean correlators using the Hansen–Lupo–Tantalo (HLT) method. The unsmeared spectral density is then obtained by extrapolating in the smearing width, and results from several ensembles with different lattice spacings are combined to perform a controlled continuum limit.
We present first applications of this strategy and discuss future directions for obtaining continuum results for $\Pi(Q^2)$ with competitive precision for electroweak observables.

Speaker: Adrián del Pino Rubio (University of Zaragoza)

89 Comparing RM123 and dynamical QCD+QED approaches to the HVP with Nf =1+2+1 Wilson fermions and C-periodic boundary conditions

Isospin-breaking corrections to the HVP are among the leading sources of uncertainty in the Standard Model prediction of the muon g−2 [1]. In recent work by the RC* collaboration [1], we compute the intermediate window contribution for a flavour non-singlet current using two strategies to include isospin-breaking corrections: the RM123 approach and a fully dynamical QCD+QED simulation. In both computations, we use C-periodic spatial boundary conditions to ensure that locality, gauge invariance, and translational invariance are preserved throughout the calculation. At fixed lattice spacing and volume with Nf =1+2+1 dynamical fermions, and fully including sea-quark effects in both computations, we find that simulating the full QCD+QED distribution yields smaller uncertainties for a fixed statistics. I will present the comparison of the two approaches and discuss the implications for future lattice QCD+QED computations.

[1] arXiv:2505.21476 [hep-ph]
[2] arXiv:2506.19770v1 [hep-lat]

Speaker: Marina Krstic Marinkovic (ETH Zurich)

90 Isospin-breaking corrections in hadronic cross sections and tau decays

Control over isospin-breaking corrections is an important requisite for the evaluation of hadronic contributions to the anomalous magnetic moment of the muon, both regarding the isospin rotation of hadronic tau decays and the comparison of data-driven evaluations of hadronic vacuum polarization with lattice QCD. In both cases, a key point concerns the definition of the isospin scheme. I will discuss recent work aimed at improving the required matching procedure.

Speaker: Martin Hoferichter

QCD at nonzero temperature and density

91 Unscreened potential and charmonium width from lattice QCD

We present our latest results on charmonium states $J/\psi(1S)$, $\psi(2S)$, $\eta _c(1S)$, $\eta _c(2S)$, $\chi _{c0}(1P)$ and $\chi _{c1}(1P)$ above the pseudo-critical temperature, using extended operators [1] on $N_x=64$, $N_\tau =16-32$ HISQ lattices using Wilson Clover fermions.

The charmonium states at zero temperature are well described by the heavy quark anti-quark potential. At finite temperature, screening of the heavy quark anti-quark potential was suggested as the cause of quarkonium melting in quark gluon plasma (QGP). Perturbative QCD calculations within potential non-relativistic QCD (pNRQCD) on the other hand do not lead to a screened potential in general, and the thermal correction to the potential also has an imaginary part.

Using extended operators, we are able to project much better into the lowest states of interest, which is needed due to the short extent in temporal direction at finite temperature, which otherwise is obscured by the continuum contribution. These results show a picture of no shift in the overall energy of the charmonium states, similar to the results from NRQCD for bottomonium [2] or for the potential extracted from Wilson line correlators [3].

Instead, all of these results show a picture of the spectral function broadening as the temperature increases, and the distance between the quarks increases. We use the vacuum wave function of different charmonium states and the imaginary part of the potential obtained by us on the lattice [3] to estimate the size of in-medium widths of $J/\psi(1S)$, $\psi(2S)$, $\eta _c(1S)$, $\eta _c(2S)$, $\chi _{c0}(1P)$ and $\chi _{c1}(1P)$ at finite temperature and compare with lattice results.

[1] Rasmus N. Larsen, Peter Petreczky, work in progress

[2] Rasmus N. Larsen, Stefan Meinel, Swagato Mukherjee, Peter Petreczky, Phys. Lett. B 800 (2020), 135119

[3] Alexei Bazavov, Daniel Hoying, Rasmus N. Larsen, Swagato Mukherjee, Peter Petreczky, Alexander Rothkopf, Johannes Heinrich Weber, Phys. Rev. D 109 (2024) 074504

Speaker: Rasmus Larsen (Bielefeld University)

92 Understanding the spin-spin interactions among heavy quarks at finite temperature

In this work we calculate the non-perturbative potential between a heavy quark and an anti-quark pair in a QCD plasma at finite temperature. Extracting the leading order static potential $V_s(r)$ from the temporal Wilson line correlators we then calculate the spin dependent component $V_{ss}(r)$ at $\mathcal{O}(1/M^2)$, using color-magnetic field insertions. The computations have been performed for quenched QCD, at $1.2, 1.5$ times the deconfinement temperature $T_d$, on a 4D lattice
with spacing $a=0.026$ fm, spatial extent $N_s=68$ and temporal size $N_\tau=16, 20$ and compared with a zero temperature calculation at $\approx 0.25 ~T_d$, on a $32^4$ lattice. We show that $V_{ss}(r)$ develops an imaginary part at finite temperature, a similar phenomenon observed in the static potential. Reconstructing the quarkonium spectral functions for both pseudo-scalar and vector channels using the spin-dependent non-perturbative potential we observe different decay widths of these states. We discuss the physical implications of our study for understanding the melting of quarkonium bound states in the quark-gluon plasma.

Speaker: Swagatam Tah (The Institute of Mathematical Sciences)

93 Color electric field correlators for diffusion of heavy quarkonia in a gluon plasma

The diffusion of a heavy quarkonium in a strongly interacting plasma can
be described, using a nonrelativistic effective field theory formalism,
in terms of transport coefficients related to the
correlators of color electric fields connected by adjoint Wilson lines.
These transport coefficients are important for the calculation
of quarkonia suppression in the plasma. We present a lattice calculation
of these correlators for the SU(3) gluon plasma. Both the
multilevel formalism and the gradient flow were used.
We compare the nonperturbative correlators with the NLO
perturbative results.
We also compare these correlators with the color electric
field correlators used for the study of heavy quark diffusion
in the plasma.

Speaker: Saumen Datta

94 Quarkonium in non-zero isospin chemical potential environment at $T \simeq 0$

We investigate how quarkonium states are affected by a medium with non-zero isospin chemical potential at near zero temperature. We obtain quarkonium correlators from heavy quark propagators which are calculated via lattice Non-Relativistic QCD (NRQCD) on the gauge field ensembles simulated with non-zero isospin chemical potential. Here, the gauge field ensemble with $\mu_I a = 0.000, 0.048, 0.053, 0.059, 0.066, 0.080, 0.092$ and $0.106$ on a $32^3 \times 48$ lattice, where $m_\pi = 135$ MeV and $a = 0.1535$ fm, are used.

Speaker: Se Yong Kim (Sejong University (KR))

Structure of hadrons and nuclei

Convener: Kehfei Liu

95 The gluon and x-dependent isoscalar quark structure of the nucleon

The HadStruc Collaboration is engaged in a long-term program to extract the partonic structure of hadrons from first principles. I will review our on-going work on the gluon momentum fraction and the x-dependent isoscalar quark structure of the nucleon. The gluon momentum fraction is central to understanding the origin of mass in hadrons and a benchmark quantity for lattice calculations of hadron structure, although lattice results are significantly less precise than current experimental data. We apply the gradient flow along with distillation and the summed generalised eigenvalue problem to improve our signal-to-noise ratio and extract the gluon momentum fraction with as high a precision as possible. For the isoscalar quark parton distribution function, I will present our computation using the pseudo-distribution framework on a single ensemble of Nf = 2+1 Wilson-Clover fermions.

Speaker: Christopher Monahan

96 The hadronic tensor from four-point functions on the lattice

The hadronic tensor is the central non-perturbative object in the calculation of the cross section of lepton-hadron interactions like neutrino-nucleon scattering. It is usually parameterized in terms of structure functions, which encode all necessary information independently of the kinematic region. Moreover, the hadronic tensor can be factorized in terms of parton distribution functions (PDFs) and contains information on hadron resonances. On the lattice, we can calculate the corresponding matrix element of two quark-bilinear currents with a relative Euclidean time separation. The reconstruction of the hadronic tensor requires appropriate dealing with the corresponding inverse problem. In our current work on the nucleon, we calculate the required four-point functions in a brought kinematic region using a clover fermion ensemble at pion mass $m_\pi = 223~\mathrm{MeV}$ and lattice spacing $a=0.0856~\mathrm{fm}$. In this talk, I will give an overview of our simulation and present some first preliminary results.

Speaker: Christian Zimmermann (University of Kentucky)

97 Higher Moments of Parton Distribution Functions from Lattice QCD at the Physical Point

Using forward matrix elements of local leading twist operators, we present a determination of the third Mellin moments $\left< x^2 \right>$ of nucleon's unpolarized, polarized and transversity parton distribution functions.
Two lattice QCD ensembles at the physical pion mass are used: these were generated using a tree-level Symanzik-improved gauge action and $2+1$ flavor tree-level improved Wilson Clover fermions coupling via 2-level HEX-smearing.
Leveraging a wide set of interpolating operators, two extraction methods for the matrix elements, data driven priors to control excited states in multi-states fits, and the automatic inclusion of model uncertainties via bootstrapped model averages, we are able to extract competitive values of the third Mellin Moments that we can compare to previous lattice results.
The data analysis procedure is explained and the obtained results are discussed.

Speaker: Emilio Taggi (Forschungszentrum Juelich, Bonn University)

98 Moments of non-singlet pion PDFs up to <x^5> using gradient flow

PDFs are universal functions appearing in factorizations of various processes relevant to collider phenomenology; many methods exist to determine their $x$ dependence in lattice QCD, but precision determinations remain challenging. Mellin moments of PDFs can be defined in terms of matrix elements of local operators in lattice QCD, but direct determinations besides $<x>$ run into challenges because of the reduced symmetry of the hypercubic lattice. We demonstrate the efficacy of a recently proposed method [1] to resolve these challenges using the gradient flow, and present ratios of flavor non-singlet PDF moments up to $<x^5>$, using four ensembles with $m_{\pi} \simeq 411~\text{MeV}$ generated by the OpenLat initiative [2]. The moments and reconstructed PDF agree quantitatively with recent phenomenological extractions.

[1] A. Shindler, Phys. Rev. D 110, L051503 (2024)
[2] https://openlat1.gitlab.io

Speaker: Dimitra Pefkou

Theoretical developments and applications beyond Standard Model

Convener: Dipankar Chakrabarti (IIT Kanpur)

99 Conserved non-singlet charges for staggered fermion Hamiltonian in 3+1 dimensions

We study conserved charges for the 3+1 D staggered fermion Hamiltonian.
In addition to $\mathrm{U}(1)_V$ charge $Q_0$, we find that the system has three independent non-singlet charges $Q_{x_i}$ $(i=x,y,z)$ that generate axial $\mathrm{SU}(2)_A$ transformations in the continuum limit. On the lattice, these charges do not commute with $Q_0$, signaling a mixed anomaly between $\mathrm{U}(1)_V$ and the subgroups $\mathrm{U}(1)_F$ of $\mathrm{SU}(2)_L \times \mathrm{SU}(2)_R \times \mathrm{U}(1)_A$.
We show that this anomaly becomes trivial in the continuum by analyzing the lattice Ward–Takahashi identity associated with $\mathrm{U}(1)_F$.

Speaker: Tetsuya Onogi (The University of Osaka)

100 Generalization of lattice Dirac operator index

By employing K-theory to classify the Wilson Dirac operator on a lattice, we give a comprehensive formulation for various indices via its spectral flow. While the index of the overlap Dirac operator, which utilizes the Ginsparg-Wilson relation, is limited to flat tori in even dimensions, our formulation offers several key advantages: 1)It is straightforward to apply to the Atiyah-Patodi-Singer index for manifolds with boundaries. 2)The boundary can be curved, allowing for the inclusion of gravitational effects. 3)The mod-2 index in even and odd dimensions can be defined as a natural extension. In the talk, we describe its mathematical proof and give some numerical examples.

Speaker: Hidenori Fukaya (The University of Osaka)

101 How to formulate the $\mathbb{Z}_8$ topological invariant of Majorana fermion on the lattice

Topological invariants and their associated anomalies have played a crucial role in understanding low-energy phenomena in quantum field theories. In lattice gauge theory, the standard $\mathbb{Z}$-valued Atiyah–Singer index is formulated via the overlap Dirac operator through the Ginsparg–Wilson relation, but extensions to more general topological invariants have remained limited. In this work, we propose a lattice formulation of the Arf–Brown–Kervaire (ABK) invariant, which takes values in $\mathbb{Z}_8$. The ABK invariant arises in Majorana fermion partition functions with reflection symmetry on two-dimensional unoriented manifolds, and its definition involves an infinite sum over Dirac eigenvalues that must be properly regularized. By carefully treating the boundary conditions, with and without a domain-wall mass term, we demonstrate that the ABK invariant can be extracted from Pfaffians of the Wilson Dirac operator. We further provide numerical verification on two-dimensional lattices, showing that the $\mathbb{Z}_8$-valued results on the torus, Klein bottle, real projective plane, and Möbius strip agree with those in the continuum theory.

Speaker: Sho Araki (The University of Osaka)

102 Spin-taste representation of Karsten-Wilczek fermions

Minimally doubled fermions realize one pair of Dirac fermions on the lattice. Similarities to staggered fermions exist, namely, spin and taste degrees of freedom become intertwined, and a peculiar nonsinglet chiral symmetry and ultralocality are maintained. However, charge conjugation, some space-time reflection symmetries and isotropy are broken by the cutoff.
We address the most simple variant, Karsten-Wilczek fermions, and derive the correct spin-taste representation from first principles. The spin-taste representation on the quark level permits construction of local or extended hadron interpolating operators for any spin-taste combination, albeit with contamination by parity partners and taste-symmetry breaking. We classify hadron interpolating operators and the Noether currents. We also discuss appropriate discretizations for taste-singlet or -isovector mass or chemical potential terms.
We explain the counterterms in this spin-taste framework, and derive generic constraints on the parametric form and cutoff effects from the KW determinant and hadronic correlation functions. We derive how and why nonperturbative tuning schemes for the counterterms work, and obtain analytic, assumption-free, nonperturbative predictions for taste-symmetry breaking and other hadronic properties from first principles. In particular, we identify the origin and nature of two different types of taste-symmetry breaking cutoff effects. The few available numerical results for KW fermions validate these predictions.

Speaker: Johannes Heinrich Weber (Technische Universität Darmstadt)

Vacuum structure and confinement

103 Neural-network parametrized ground state optimization for the static quark-antiquark pair

The extraction of the static quark-antiquark potential from lattice QCD suffers from the poor signal-to-noise ratio of Wilson loops at large Euclidean times. To overcome this, smearing methods or the Coulomb gauge are used to improve the ground-state overlap with respect to the straight Wilson line trial state within the Wilson loop. We introduce a neural-network parametrization of trial states, constructed with gauge-equivariant layers and optimized with a loss function that favors the ground state. In quenched theory, our method achieves improved overlap compared to standard Wilson loops and is competitive with Wilson line correlators in Coulomb gauge. We further extend the framework to access excited states and outline a systematic strategy for their extraction.

Speaker: Julian Mayer-Steudte

104 Entanglement as a Probe of Flux Tube Structure

We study the entanglement entropy of flux tubes in SU(N) (2+1)-D pure gauge theory, using it as a probe of their internal structure. Through analyzing flux tube entanglement entropy across different spatial bipartitions, we extract quantitative information about the color flux tube's substructure, including its intrinsic width and its dependence on $N_c$. We compare our results to the expectations of various effective models and discuss their broader implications.

Speaker: Rocco Amorosso

105 Entanglement Entropy in Lattice Gauge Systems from a Dual Loop Formulation

We study the problem of defining and computing entanglement entropy in lattice gauge systems using a dual loop formulation. The main idea is to apply a sequence of canonical transformations that rewrite the standard link variables of $SU(2)$ and $U(1)$ lattice gauge theories in terms of the loop variables. This allows an easier handling of gauge-invariant degrees of freedom and gives a cleaner way to define subsystems on the lattice. We work in spin-network basis and test the construction on simple states to understand how the reduced density matrix can be defined in this framework. The analysis is general for $SU(2)$ and $U(1)$. The work is still in progress, and I plan to present the structure of the formulation, along with some preliminary results and open issues.

Speaker: Adarsh S. (National Institute of Technology Calicut)

106 Phase diagram of 4D SU(3) Yang-Mills theory at $\theta = \pi$ via imaginary theta simulations

It has been predicted that the CP symmetry of the 4D SU(3) Yang-Mills theory at $\theta = \pi$ is spontaneously broken in the confined phase, and it is recovered precisely at the deconfining temperature.
The direct simulation of the theory at $\theta = \pi$ is, however, difficult due to the sign problem.
Thus, we simulate the theory with an imaginary theta parameter and perform analytic continuation to the real theta to study the phase diagram.
We implement the stout smearing technique in the hybrid Monte Carlo simulation to recover the topological property of the gauge field.
The smearing-time dependence of the observable is investigated using the reweighting method with respect to the smearing step parameters, and a clear scaling behavior is observed.
The order parameter of the CP symmetry is then computed in the scaling region to detect symmetry breaking.
We report preliminary results of the expected CP breaking and restoration temperature.

Speaker: Akira Matsumoto (Graduate School of Science, Osaka Metropolitan University)

16:10 Coffee break

Hadronic and nuclear spectrum and interactions

Convener: Fernando Romero López (Uni Bern)

107 Two-particle matrix elements in a box

Resonant hadrons, and some loosely bound states, can be studied by looking at the energy dependence of the reaction rate of the multi-particle asymptotic states associated to them. For instance, the form factors of these states can be found via analytic continuation of the two-particle transition rate induced by the current of interest. These transitions, in turn, can be constrained from finite volume spectra and matrix elements, which can be obtained from a lattice calculation. In this talk we will describe the procedure to connect finite volume data to infinite volume transitions, and apply it to a non-relativistic toy model lattice theory. This toy model features a bound state whose binding energy can be tuned from a state close to threshold to deeply bound. We find that the finite volume effect in matrix elements becomes more significant as the binding energy decreases. Finally, we show that these effects can be corrected with the framework describing the volume dependence of the nearby two-particle channel.

Speaker: Felipe Ortega Gama (UC Berkeley)

108 Bayesian Analysis and Analytic Continuation of Scattering Amplitudes from Lattice QCD

We present a novel procedure for analyzing the lattice-QCD spectrum via the finite-volume formalism to obtain constraints on multi-hadron scattering amplitudes at both real and complex energies. This approach combines a Bayesian reconstruction of the scattering amplitude on the real axis with Nevanlinna interpolation for analytic continuation to complex-valued energies. The method is non-parametric, inherently accounting for parametrization dependence within the uncertainty. We demonstrate the applicability of this approach using real lattice-QCD data.

Speaker: Miguel Salg (University of Bern)

109 Towards four-pion effects in multi-hadron decays

Four-particle intermediate and final states pose major challenges for lattice calculations of scattering and decay amplitudes, as well as long-distance matrix elements. As a step toward addressing these challenges, we present preliminary results from a perturbative study of four-pion effects in finite-volume spectra and in the relation between finite-volume matrix elements and decay amplitudes. Although our approach does not capture all volume effects or provide a full connection to the scattering amplitude, it includes the leading $2\to2$ and $2\to4$ contributions and reproduces two- and four-pion–like avoided level crossings in the finite-volume spectrum. We also discuss the implications of these findings for hadronic $D$ decays and for four-particle effects in the hadronic vacuum polarisation contribution to $(g-2)$.

Speaker: Rajnandini Mukherjee (University of Edinburgh)

QCD at nonzero temperature and density

110 Towards a Determination of thermal static Potential at Finite Density from Lattice QCD

The modification of heavy-quark interactions in hot and dense QCD matter plays a central role in understanding the fate of quarkonium in heavy-ion collisions. While lattice QCD studies at zero chemical potential have established the temperature dependence of the static quark–antiquark potential and its spectral properties, the finite baryon density regime remains largely unexplored. In this work, we investigate the potential between static quarks at nonzero baryon chemical potential using Taylor-expanded Wilson line correlators. Simulations are carried out in (2+1)-flavor QCD at physical quark masses with the HISQ action on ensembles generated by the HotQCD collaboration. This study provides first steps toward connecting lattice QCD results for the heavy-quark potential to quarkonium survival probabilities in the QCD phase diagram at finite density, with direct relevance to current and upcoming experiments at RHIC and FAIR.

Speaker: Jishnu Goswami (Bielefeld University)

111 Shear Viscosity: Renormalization of the EMT in Full QCD

The determination of shear viscosity in quark-gluon plasma from first principle has remained one of the most challenging problems for decades, despite its significant importance in research fields such as hydrodynamics and cosmology. It has been studied in pure-glue theory on the lattice, but its investigation in full QCD is particularly complex. One of the main reasons for this complexity is the renormalization of the energy-momentum tensor (EMT) on the lattice. In this work, we use the gradient flow method to construct the renormalized EMT. In full QCD, the shear viscosity requires one extra renormalization coefficient, arising from the fermionic component of the EMT. We use enthalpy density to fix these renormalization coefficients using an imaginary isospin chemical potential. We measure the number density to obtain the pressure and then the interaction measure to determine the enthalpy density on the lattice. The corresponding EMT component is then measured to fix the lattice renormalization. Finally, we report progress on extracting the renormalization coefficients and discuss their connection to shear viscosity.

Speaker: Pavan Pavan

112 Spectral reconstruction techniques, their shortcomings and relevance to the electric conductivity coefficient

We study spectral reconstruction techniques to obtain the electric conductivity coefficient at non-zero external magnetic fields for Wilson fermions in quenched QCD from the euclidean correlator. Spectral reconstruction is a well studied numerically ill-posed problem which arises due to the relation of the euclidean correlator to the spectral function via an inhomogenous Fredholm equation of the first kind. Several different methods are on the market to resolve this issue, each taking different approaches and assumptions. The aim of this talk is to compare some of the reconstruction techniques including machine learning methods on mock data to spot systematic errors and shortcomings of certain reconstruction techniques. We then apply the reconstruction techniques to lattice simulation data to extract the spectral function. The behaviour of the spectral function at frequencies approaching zero then gives the electric conductivity coefficient via a Kubo formula.

Speaker: Christian Andratschke (Bielefeld University)

113 Spectral reconstruction and dimensional reduction in high-temperature gauge theories

Measurements of real-time spectral functions (such as e.g. electric AC conductivity) in lattice gauge theory simulations usually rely on a numerically ill-defined analytic continuation of lattice correlation functions from imaginary (Euclidean) to real (Minkowski) frequencies. With only Euclidean correlators as input, this procedure has fundamentally limited frequency resolution of order of pi*T. On the other hand, at sufficiently high temperatures gauge fields become almost classical and practically do not depend on Euclidean time, effectively reducing to three-dimensional static fields. We demonstrate that at sufficiently high temperatures, finite-temperature dimensional reduction allows to extract much more information on fermionic spectral functions from Euclidean-time Monte-Carlo simulations. With a good precision, spectral functions can be calculated for a single fermion moving in the background of static, disordered gauge fields, which is a polynomial-complexity problem. We first test this approach in 1+1-dimensional U(1) lattice gauge theory with dynamical fermions and demonstrate excellent agreement with spectral functions calculated from exact diagonalisation of the full quantum Hamiltonian. We then demonstrate that dimensional reduction also works well for Euclidean-time meson correlators in high-temperature lattice QCD.

Speaker: Pavel Buividovich

Software development and machines

Convener: Carleton DeTar (University of Utah)

114 Variance Reduction with Probing and Multilevel Monte Carlo in Lattice QCD

Trace estimation in lattice QCD benefits from two complementary variance-reduction techniques: probing methods that exploit operator structure, and multigrid multilevel Monte Carlo, an efficient deflation technique. We propose a unified framework that combines these ideas and evaluate it on three representative targets: the trace of the inverse of the Dirac operator, traces entering the connected pseudoscalar correlator, and disconnected fermion loops. Multigrid multilevel Monte Carlo achieves deflation using a projector derived from the multigrid prolongator $P$, which captures low-mode information of the Wilson–Dirac operator. Probing is implemented by applying distance-$d$ graph colorings to the lattice, which exploit locality to suppress off-diagonal noise. Within each lattice site, further restricting the noise vectors to subsets such as spin or color is referred to as dilution. We observe systematic variance reductions across all problems, with the disconnected case in particular profiting from the complementary strengths of deflation and probing.

Speaker: Jose Miguel Jimenez Merchan (Bergische Universität Wuppertal)

115 Improving HISQ Propagator solves using multigrid

The conjugate gradient (CG) algorithm, employing mixed precision and even-odd preconditioning, is typically used when computing propagators for highly improved staggered quarks (HISQ). However, its performance degrades due to critical slowing down as the light quark mass approaches its physical value. In previous work, we addressed this issue using deflation, which significantly reduced solve times—achieving speedups of up to 10$\times$ over CG on the most challenging ensembles, albeit with a substantial setup cost to compute eigenvectors. In this work, we focus on a multigrid algorithm for HISQ propagators tuned to achieve optimal performance. Multigrid achieves even greater speedups—up to 17$\times$—nearly doubling the speedups achieved with deflation—while substantially reducing both the setup cost and the memory resources required. We present benchmarks using the MILC and QUDA software libraries on lattices up to $144^3×288$ (lattice spacing 0.04 fm) and quark masses ranging from the physical strange down to the physical light quark values. We compare CG, deflation, and multigrid, highlighting the trade-offs between setup cost, memory footprint, and overall solve-time savings.

Speaker: Leon Hostetler (Indiana University)

116 Could photonic integrated circuits have an impact on lattice QCD?

Lattice quantum chromodynamics (LQCD) calculations are pushing the limits of today’s most powerful supercomputers. Since most resources are consumed in solving large systems of linear equations, efficient solvers, such as those based on adaptive multigrid methods, are essential. However, with the slowdown of Moore’s Law, it is uncertain whether traditional architectures can deliver the computational power and energy efficiency needed for future LQCD computations. In this talk, we explore photonic computing as a promising emerging paradigm to extend performance in the post-Moore’s Law era. By using photons instead of electrons, photonic processors enable ultra-low latency and energy-efficient matrix operations. To deal with the limited precision of the analog hardware, we introduce a mixed-precision photonic (MPP) solver based on multigrid methods, and present tests on a simple discretized partial differential equation as well as an emulated MPP solver applied to the 2D U(1) Schwinger model. Potential performance gains in both speed and energy efficiency are estimated to reach an order of magnitude, highlighting the potential of domain-specific photonic hardware to accelerate future LQCD calculations.

Speaker: Timoteo Lee (University of Heidelberg)

117 Lattice QCD on the NVIDIA Grace-Hopper and Blackwell Architectures

The evolution of GPU architectures has fundamentally transformed computational capabilities for Lattice QCD simulations. Over recent generations, GPU memory bandwidth has increased by approximately one order of magnitude, with modern systems achieving terabytes per second of memory throughput, while computational width has expanded significantly. These advances, driven primarily by artificial intelligence workload demands, present new optimization opportunities for Lattice QCD calculations.
We present comprehensive optimization strategies implemented in QUDA that fully exploit the potential of modern single-GPU systems. Additionally, we examine the benefits of coherent memory architectures in Grace-Hopper and Grace-Blackwell superchip platforms. Finally, we investigate strong scaling properties of Lattice QCD applications on multi-node NVLink Grace-Blackwell systems.

Speaker: Mathias Wagner (Nvidia)

Structure of hadrons and nuclei

Convener: Dimitra Pefkou

118 The Three-Dimensional Structure of the Nucleon through Lattice QCD

The HadStruc collaboration is pursuing a program aimed at understanding the three-dimensional internal structure of the nucleon encapsulated in the Generalized Parton Distributions (GPDs) and Generalized Form Factors (GFFs) within the short-distance factorization approach. I present recent work by HadStruc on the isovector GFFs of the nucleon, including those corresponding to non-zero skewness. I then present preliminary results for the reconstructed x-dependent GPDs. The calculations are performed using 2+1 flavor Wilson-Clover fermions at a pion mass of around 350 MeV, exploiting the distillation framework to provide improved sampling of the gauge configurations, and to provide greater control over the uncertainties arising from the contributions from excited states.

Speaker: David Richards (Jefferson Lab)

119 Parton physics from a heavy-quark operator product expansion: Dynamical lattice QCD calculation of moments of the pion and kaon light-cone distribution amplitude

The light-cone distribution amplitude (LCDA) is a fundamental non-perturbative quantity for understanding hadron structure. We report on our calculation of the pion and kaon LCDAs using the heavy-quark operator product expansion (HOPE) framework. This method employs an OPE analysis of hadronic amplitudes through the inclusion of a fictitious valence heavy quark, and has previously been shown to be a viable method to compute the second and fourth Mellin moments of the pion in the quenched approximation. In this talk we present preliminary results for the first three nontrivial Mellin moments of the kaon LCDA, as well as the second moment of the pion LCDA, from dynamical calculations using the CLS ensembles. This work demonstrates the feasibility of the HOPE method for accessing higher moments of meson LCDAs from lattice QCD.

Speaker: S.-P. Alex Chang (Institute of Physics, National Yang Ming Chiao Tung University, Taiwan)

120 x-dependent Light Baryon LCDAs from Lattice QCD

We present the results of lattice QCD calculation of all leading-twist x-dependent Light-cone Distribution Amplitudes (LCDAs) for baryons in light octet, within the framework of Large-momentum Effective Theory (LaMET). We implement a novel Hybrid renormalization scheme for baryon nonlocal operators, and perform simulations at 4 different lattice spacings a = {0.052, 0.068, 0.077, 0.105} fm, achieving reliable and precise results of x-dependent baryon LCDA. To access the large momentum regime and facilitate matching to light-cone, we simulate the quasi-Distribution Amplitudes (quasi-DAs) with hadron momenta Pz of about 1~3 GeV. The numerical calculations employ CLQCD ensembles with stout smeared clover fermions and a Symanzik gauge action, and several new techniques are also developed to improve the extrapolation and inversion in matching procedure. We present the resulting momentum-fraction distributions for the two light quarks in the light baryon.

Speaker: Mu-Hua Zhang (Shanghai Jiao Tong University)

121 Partonic functions in Minkowsky space with tensor networks – a Schwinger model study

The rich internal structure of hadrons is encoded in partonic functions, such as parton distribution functions (PDFs) and light-cone distribution amplitudes (LCDAs), which are crucial in collider experiments and decay processes. Calculating them from first principles remains a major challenge: they require matrix elements with a Wilson line along a light-like direction, which is not directly accessible in the Euclidean lattice formulation underlying conventional Monte Carlo simulations. In contrast, the Hamiltonian formalism allows for a direct treatment of light-cone dynamics. We present a tensor-network framework that extracts light-cone matrix elements in Minkowski space through real-time evolution of states, and show the application in the Schwinger model. We obtain PDFs and LCDAs for different fermion masses with controlled uncertainties, demonstrating the feasibility of tensor networks for dynamical calculations in gauge theories.

Speaker: Manuel Schneider (National Yang Ming Chiao Tung University)

Theoretical developments and applications beyond Standard Model

Convener: Srimoyee Sen

122 Generalizing deconfined criticality to 3d $N$-flavor $SU(2)$ quantum chromodynamics on the fuzzy sphere

The deconfined quantum critical point (DQCP) exemplifies a phase transition beyond the Landau paradigm, yet its true nature remains debated. We investigate a candidate for the $SU(2)$ QCD$_3$ theory with $N$ fermions and a $Sp(N)/\mathbb{Z}_2$ global symmetry, which is a possible effective description of the DQCP—using the recently proposed fuzzy sphere regularization. This method offers a powerful lens to probe the model’s critical behavior. Employing quantum Monte Carlo simulations of the generalized Sp(N)-symmetric model, we probe the conformal window of the gauge theories, with the fuzzy sphere formalism significantly reducing finite-size-effects.

Speaker: Emilie Huffman (Wake Forest University)

123 Critical scaling in the N=1 Thirring Model in (2+1)d

The Thirring model in 2+1d with $N$ flavors can exhibit spontaneous
U(2$N)\to\,$U($N)\otimes$U($N$) breaking through fermion - antifermion condensation in the limit $m\to0$. With no small parameter in play the symmetry-breaking dynamics is strongly-interacting and quantitative work requires a fermion formulation accurately capturing global symmetries. We present simulation results for $N=1$ obtained with Wilson kernel Domain Wall fermions on $16^3\times L_s$, with $L_s=24,\ldots,120$. The $L_s\to\infty$ extrapolation of the bilinear condensate $\langle\bar\psi\psi\rangle$ as a function of coupling and bare mass is fitted to an empirical equation of state; the resulting critical exponents are significantly altered from previously obtained values, and for the first time resemble those emerging from analytic predictions based on approximate solutions to Schwinger-Dyson equations, consistent with a putative UV-stable renormalisation fixed point. To address the non-perturbative issue of the value $N_c$ below which such a fixed point exists we present preliminary results obtained with $N=2$.

Speaker: Simon Hands (University of Liverpool)

124 Eigenstate Thermalization in 1+1-Dimensional SU(2) Lattice Gauge Theory Coupled with Dynamical Fermions

Understanding thermalization in isolated non-Abelian gauge theories is a key challenge for quantum simulation. We present a study of the Eigenstate Thermalization Hypothesis (ETH) in 1+1-dimensional SU(2) lattice gauge theory with one flavor of dynamical staggered fermions. Using the gauge-invariant Loop-String-Hadron (LSH) framework, we perform exact diagonalization on finite lattices to analyze the validity of diagonal and off-diagonal ETH for local operators, such as electric field or matter density and non-local observables, such as mesonic strings of varying length. This work provides a direct test of ETH in a non-Abelian gauge theory and establishes a benchmark for future quantum simulations of thermalization dynamics.

Speaker: Indrakshi Raychowdhury

125 Thermal SU(2) gauge theory for the pseudogap and origin of cuprate superconductivity

Cuprate superconductors, the most commonly known class of high-$T_c$ superconductors, have much richer properties than the conventional superconductors, yet much of it is not well-understood. To explain their physical origin, many theories involving emergent gauge fields have been put forth in recent years. Focusing on the theory developed in Christos et al., PNAS 120(21) e2302701120 (2023), consisting of fundamental SU(2) bosons of charge $e$ coupled to emergent SU(2) gauge fields, we develop a Monte-Carlo algorithm to efficiently sample the fluctuating gauge and boson fields in presence of finite temperature. We demonstrate a Kosterlitz-Thouless transition from the superconducting (SC) to a pseudo-gap (PG) phase and the existence of vortices with flux $h/(2e)$ confirming that indeed these arise due to confinement of the SU(2) gauge fields. Furthermore, we explicitly show the existence of a period-4 charge order nucleating inside the vortex cores, observed in the experiments by Hoffman et al., Science 295, 466 (2002). Further, we also observe Fermi arcs in the electronic spectral density in the high temperature PG phase where quantum oscillations of hole pockets with fractional area in the local electron density of states are also observed, thus unifying these seemingly unrelated phenomena within the framework of a single theory.

Speaker: Harshit Pandey (The Institute of Mathematical Sciences, Chennai)

Vacuum structure and confinement

126 Update on the computation of the unquenched Yang-Mills lattice spectrum in the 't Hooft limit

We report on the continued efforts to measure the glueball and meson spectra of Yang-Mills lattice gauge theories based on the gauge group $SU(N_c)$ in the t’Hooft limit.
We employ a multilevel sampling algorithm to measure glueball correlators to reduce statistical noise in the large time separation limit. The gluon operator basis is composed of spatial Wilson loop with vanishing momentum selected to maximise the orthonogality of the operators and the operator overlap on the lowest lying states. The Observables are measured at different levels of (APE) smearing. We discuss the performance of the algorithm and the details of the computation of the first low-lying spectrum for the gauge group $SU(6)$.

Speaker: Andrea Falzetti ("Sapienza" University of Rome)

127 Direct numerical simulation of 't Hooft partition function and (de)confining phase

We propose a novel approach to directly simulate the 't Hooft partition function and revisit the (de)confining phase structure of an $SU(N)$ gauge theory with the $\mathbb{Z}_N$ $1$-form symmetry. We develop a hybrid Monte Carlo algorithm (the halfway HMC) for the $SU(N)/\mathbb{Z}_N$ gauge theory. The usual partition function $\mathcal{Z}[B]$ with 't Hooft flux $B$ can be numerically computed by it. By regarding spatial-temporal components of $B$ as electric fluxes $E$, the 't Hooft partition function $\mathcal{Z}_{\text{tH}}[E;B]$ detects the quantum phase of the system. The numerical result shows that non-electric fluxes are light in the confining phase, while at finite temperature a nontrivial finite-size scaling and deconfining of $\mathcal{Z}_{\text{tH}}[E;B]$ can be observed. The Witten effect also indicates the oblique confinement at $\theta=2\pi$.

Speaker: Okuto Morikawa (RIKEN iTHEMS)

128 Meson spectrum and low-energy constants in large-$N$ QCD

I will present new non-perturbative results about the meson spectrum and the low-energy constants of QCD in the 't Hooft large-$N$ limit, $N \to \infty$ with $N_{\rm f}/N \to 0$. These are obtained from lattice Monte Carlo simulations of the Twisted Eguchi-Kawai (TEK) model up to $N=841$.

More precisely, I will discuss the determination of radial Regge trajectories in the $\pi$ and $\rho$ channels; and the computation of the coefficients of the $1/N$ expansion of the chiral condensate, of the pion decay constant, and of the NLO coupling $\bar{\ell}_4$ up to $O(1/N^3)$ from the combination of TEK and standard finite-$N$ results.

Speaker: Claudio Bonanno (IFT UAM/CSIC Madrid)

Poster session

129 Antistatic-antistatic-light-light potentials and disentanglement of excited states in Lattice QCD

We report on our ongoing lattice QCD computation of antistatic-antistatic-light-light potentials using the CLS $N_f=2$ gauge configurations and the OpenQ*D codebase. We improve on previous work by calculating the correlation matrices for all three attractive ground state potentials previously characterized, to mitigate excited state contributions and further probe the vague indication of one-pion exchange at static quark separations $r\gtrsim\0.5fm$. Furthermore, we attempt to implement Wilson flow smearing at the source and sink, and we bolster our statistical analysis by taking into account autocorrelations using the pyerrors package.

Speaker: Bernardo Miguel Carvalho Rodrigues Cruz Picão (Instituto Superior Técnico)

130 Centre vortex evidence for two finite-temperature QCD phase transitions

Centre vortices have been shown to underpin confinement and dynamical chiral symmetry breaking. Here we consider the centre vortex geometry of dynamical QCD at finite temperature using the anisotropic FASTSUM ensembles and uncover evidence for two transition temperatures. The first corresponds to the established chiral transition $T_c$ while the second occurs at $T_d\simeq 2\,T_c$. Drawing upon visualisations of the centre vortex structure and statistical analysis of vortex density and cluster extent, we interpret this second transition as the deconfinement transition.

Speaker: Ryan Bignell (Trinity College Dublin)

main.pdf

131 Cut-off effect analysis of the covariant coordinate space method for vacuum polarization calculations in lattice regularization

The covariant coordinate space (CCS) method for hadronic vacuum polarization calculations has been developed as an alternative to the established time-momentum representation (TMR) and is particularly promising for its potential to mitigate statistical noise. Our investigations further reveal that this framework exhibits a favorable continuum limit. We provide an extensive analysis of the cut-off effects to leading order in lattice perturbation theory. We analyze the issue of $a^2 log(a)$ artefacts which typically complicate continuum extrapolations. In combination with the inherent flexibility of the integration kernel, we see an overall superior quality of the CCS continuum limit. We expect our insights to be helpful also for other lattice calculations of high-precision observables and that coordinate space methods may be advantageous for such computations.

Speaker: Cornelia Tölle (Johannes Gutenberg-Universität Mainz)

Toelle_AnalysisCCS_Lattice2025.pdf

132 Duality and disorder operators in SU(N) Lattice Gauge Theory

We construct an exact dual formulation of pure SU(N) Hamiltonian lattice gauge theory with local dual dynamics in (2+1) dimensions. The dual model is obtained by making a series of iterative canonical transformations on the electric field operators and their conjugate vector potentials associated with the links around each plaquette. This transformation maps the original gauge degrees of freedom to dual variables defined on plaquettes: SU(N) magnetic scalar fields corresponding to plaquette flux operators, and their conjugate electric scalar potentials. Under SU(N) gauge transformations, both transform like adjoint matter fields. The dual Hamiltonian describes the nonlocal self-interactions of these plaquette flux loops in terms of the electric scalar potentials and with inverted coupling. We show that these nonlocal loop interactions can be made local and converted into minimal couplings by introducing SU(N) auxiliary gauge fields along with
new plaquette constraints. Our construction completely simplifies the magnetic part of the Hamiltonian, which dominates near the continuum (g² → 0) limit.

Exploiting these exact duality transformations, we construct the most general disorder operator for SU(N) lattice gauge theory. These disorder operators, defined on the plaquettes and characterized by (N-1) angles, are the creation and annihilation or the shift operators for the SU(N) magnetic vortices carrying (N-1) types of magnetic fluxes. They are dual to the SU(N) Wilson loop order operators which, on the other hand, are the creation-annihilation or shift operators for the (N-1) electric fluxes on their loops. We derive a new order-disorder algebra involving SU(N) Wigner-D matrices that reduce to standard Wilson-’t Hooft algebra in a special limit. We also compute the path integral expression for the vortex-free energy, which should be useful for Monte Carlo simulations and to understand the role of magnetic vortices and their condensation, if any, in the colour confinement.
References:
1. Manu Mathur, Atul Rathor , Exact Duality and Local Dynamics in SU(N ) Lattice Gauge Theory, Phys. Rev. D 107, 074504 (2023).
2. Manu Mathur, Atul Rathor, Disorder Operators and Magnetic Vortices in SU(N) Lattice Gauge Theory, Phys. Rev. D 108, 114507 (2023).

Speaker: Atul Rathor (S N Bose National Center for Basic Sciences, Kolkata-700106)

133 Efficient Low-Mode Averaging for Meson and Baryon Correlators at the Physical Point

We present an analysis of deflation and low-mode averaging techniques applied to two- and three-point correlation functions of mesons and baryons at the physical point. The focus is on improving the signal quality at large Euclidean time separations, where statistical noise typically dominates. We quantify the computational cost and statistical gains across several ensembles, identifying the regimes where low-mode averaging provides a net advantage. Practical strategies for implementing the method efficiently in large-scale simulations are discussed, with emphasis on the balance between eigenmode computation and correlator improvement. Our results demonstrate clear benefits in selected observables and provide guidelines for the optimal use of low-mode techniques in precision lattice QCD calculations.

Speaker: Antonio Evangelista (University and INFN of Rome Tor Vergata)

134 Enhanced Sampling Techniques for Lattice Gauge Theory

In theories with topological sectors, such as lattice QCD and four-dimensional SU(N) gauge theories with periodic boundary conditions, conventional update algorithms suffer from topological freezing due to large action barriers separating distinct sectors. With appropriately constructed bias potentials, Metadynamics and related enhanced sampling techniques can mitigate this problem and significantly reduce the integrated autocorrelation times of the topological charge and associated observables.

We test strategies to accelerate the buildup of bias potentials and the possibility of extrapolating potentials from small to large volumes. We also investigate the effectiveness of orthogonal algorithmic improvements, such as longer HMC trajectories and HMC variants, which may benefit conventional simulations as well.

Speaker: Timo Eichhorn (University of Wuppertal)

135 Evaluation of Numerical Methods for the Quark Propagator

Recent advances in numerical algorithms for matrix function evaluations have significantly improved the stability and efficiency of large-scale computations in quantum field theory. In this study, we investigate their applicability to the calculation of the quark propagator in lattice QCD. The quark propagator, which involves the inversion and functional evaluation of large sparse matrices derived from the Dirac operator, poses a stringent test for numerical precision and algorithmic robustness. We compare several iterative and polynomial-based approaches, including Krylov subspace and rational approximation methods, focusing on their convergence behavior and numerical stability under realistic lattice conditions. Our results demonstrate how recent developments in numerical linear algebra can enhance the accuracy and reliability of quark propagator computations, providing valuable insights for future high-precision studies in lattice gauge theory.

Speaker: Chiho Nonaka (Hiroshima University)

136 Highly improved staggered quarks in the Grid framework

For nearly two decades, the highly improved staggered quark (HISQ) discretization of the Dirac operator has enabled fast and accurate simulations of (2+1)- and (2+1+1)-flavor QCD, particularly at the physical point. Over this period, numerous code bases targeting both CPU and GPU architectures have implemented HISQ through a variety of methods that optimize for low communication overhead, efficient use of local storage, programmatic flexibility, and so forth. We discuss ongoing efforts targeting a single-source implementation of the HISQ smearing and derivatives within the Grid framework. We emphasize our use of Grid's GeneralLocalStencil and PaddedCell data structures for the purpose of minimizing both communication overhead and storage costs. Additionally, we discuss Grid-specific design choices that enhance the flexibility of our implementation of HISQ while improving Grid's present staggered infrastructure. We end with a timeline for production-readiness and future applications, such as domain-decomposed hybrid Monte Carlo.

Speaker: Curtis Peterson (Michigan State University)

137 Investigation of a novel fully relativistic heavy-quark action in $D$ meson systems

We present initial results for the application of a novel relativistic heavy-quark action in the charm sector on 2+1-flavor lattice ensambles produced by the CLS consortium. The five parameter action was tuned non-perturbatively using a neural network and experimental continuum charmonium ground state masses. We investigate effective masses of $D$ meson correlators produced on CLS ensambles X451 and N451 with pion mass of approximately 280 MeV, as well as the expected relativistic dispersion relation. The meson correlators were produced using the stochastic distillation scheme. Additionally we present expected energy levels of the $D\pi$-channel in meson-meson scattering up to the $\eta$ threshold and describe our setup for an ongoing determination of scattering amplitudes in the $D\pi$ scattering system.

Speaker: Mr David Thoma (Technische Universität Darmstadt(TUDA-IKDA))

138 Lattice artifacts proportional to the quark mass in the QCD running coupling

In this work, we investigate discretization effects proportional to the quark mass, $O(a m)$, on the QCD beta-function within lattice perturbation theory. Using the background field method and improved lattice actions, we compute the renormalization factor of the coupling constant and thus determine the beta-function. In this framework, we calculate, up to two-loop order, the contributions proportional to the quark mass arising in the background gluon propagator. The number of colors $N_c$ and the number of quark flavors $N_f$ are kept arbitrary throughout the calculation. We employ clover fermions together with Symanzik-improved gauge actions, involving Wilson loops with 4 and 6 links. This allows us to isolate the lattice artifacts that affect the determination of the running coupling. The removal of these effects is essential for high-precision, non-perturbative determinations of the strong coupling constant from lattice simulations.

Speaker: Dr Demetrianos Gavriel (University of Parma, INFN Parma, University of Cyprus)

Lattice2025_poster_Demetrianos_Gavriel.pdf

139 Lattice studies of entanglement entropy in O(N) models at finite densities

Despite their simplicity, O(N) scalar field theories, or O(N) models for short, allow for the investigation of several interesting phenomena such as asymptotic freedom and spontaneous symmetry breaking. On the lattice, O(N) models can be represented in terms of integer-valued flux variables, which allow for efficient Monte Carlo (MC) simulations both at zero and non-zero densities with a worm algorithm.

As a characteristic property of all quantum systems, entanglement provides a novel way to study different QFT phenomena. In recent years, significant progress has been made in lattice computations of entanglement measures such as entanglement entropy (EE).

In my poster, I will present our approach in incorporating evaluations of EE using the replica trick into MC simulations of O(N) models at finite density with the worm algorithm and showcase our results on how the derivative of EE w.r.t. the width of the entanglement region changes as a function of both the density and the width itself.

Speaker: Aatu Rajala (University of Helsinki)

Lattice2025_Poster_Rajala.pdf

140 Lattice study of RG flow in 2D phi4 theory

In two dimensions, the phi4 theory exhibits a non-trivial infrared fixed
point that governs the continuum limit and connects to the Ising universality class. I will present the investigation of RG flow of 2D phi4 theory using gradient flow techniques, with smooth lattice configurations and allow for a non-perturbative definition of scale-dependent observables. By tracking the evolution of operators under gradient flow, signatures of the the non-trivial fixed point can be identified.

Speaker: Shashank Sharma (Institute of technology in Kanpur)

141 Multicritical Behavior in a Three-Dimensional Gross–Neveu Model with Staggered Fermions

We study the phase diagram of massless staggered fermions with two distinct four-fermion couplings, U and U′, on a three-dimensional Euclidean lattice using the fermion-bag Monte Carlo method. The model exhibits three distinct phases: a massless fermion phase, a symmetry-broken massive phase with a fermion bilinear condensate, and a symmetric massive phase where fermions acquire mass without spontaneous symmetry breaking. We find that a nonzero U introduces an intermediate symmetry-breaking phase, turning the direct exotic transition at U=0 into two conventional critical lines: a mean-field (Gross–Neveu–type) transition between the massless and broken phases, and a 3D XY transition between the broken and symmetric massive phases. Our results suggest these critical lines may meet at a multicritical point with enhanced symmetry.

Speaker: Debasish Banerjee (University of Southampton)

142 Online or in person?

We present results from our DEI surveys conducted in 2023 and 2024, focusing on whether workshops should be held online or in person. Surprisingly, we find no correlation between diversity criteria and a preference for online conferences, including care responsibilities. The only numerically significant predictors that lead scientists to prefer an online conference, as shown in new survey data from 2024, are VISA waiting times and lack of funding. Improved support for visa acquisition and funding can help improve the possibility of attendance.

Speaker: Sofie Martins (University of Graz)

143 Overcoming ergodicity problems of HMC using radial updates

The sensible application of the Hybrid Monte Carlo (HMC) method to the Hubbard model is hindered by the emergence of infinite potential barriers due to a vanishing fermion determinant, resulting in an ergodicity problem that needs to be resolved. This can be achieved by augmenting the HMC algorithm with radial updates, which refer to multiplicative Metropolis-Hastings updates in a radial direction of the non-compact fields. These radial updates facilitate jumps over the potential barriers, thereby restoring ergodicity while simultaneously reducing autocorrelation times at a comparably low computational cost.

Speakers: Prof. Anthony Kennedy, Johann Ostmeyer (University of Bonn)

RadialUpdatesPosterCRC.pdf

144 Pion and kaon decay constants on CLS ensembles

We present results on the pion and kaon decay constants determined on a set of over 50 coordinated lattice simulations (CLS) gauge ensembles with $N_f=2+1$ sea quark flavours of non-perturbatively improved Wilson fermions. This is part of a project to explore the range of validity of SU(3) chiral perturbation theory (ChPT) in the meson sector and to determine its low energy constants (LECs). The ensembles span three trajectories of relevance to SU(2) and SU(3) ChPT in the quark mass plane: a line of almost constant strange quark mass, a line along which the trace of the mass matrix is kept constant and the flavour symmetric line of equal quark masses. The physical quark mass point is included in the set of ensembles, as are different volumes, further constraining the SU(3) ChPT LECs. The 6 distinct lattice spacings, ranging from about 0.1 fm to below 0.04 fm, allow for a controlled continuum limit extrapolation. We also investigate scale setting, using the pion decay constant as input.

Speaker: Gunnar Bali (Universität Regensburg)

poster.pdf

145 Reinforcement learning (RL) methods for finding fermion propagators

The conjugate gradient is the standard technique for computing propagators in lattice QCD. Preconditioning the Dirac Operator makes this method faster. The goal of our project is to develop Neural Networks to predict preconditioners for the Dirac operator with the gauge configuration as input.
Our approach closely follows recent successes from MIT[1], where traditional neural networks have been used to learn preconditioners by optimizing a differentiable loss function. We plan to first set up similar neural networks for 4D SU(3) gauge configurations.
The primary objective is to then develop a reinforcement learning-based neural network that achieves similar outcomes. These networks can be used to build neural networks in cases where the loss function may not be differentiable, making them a viable option for a broader range of applications.

[1] Y. Sun, S. Eswar, Y. Lin, W. Detmold, P. Shanahan, X. Li, Y. Liu and P. Balaprakash,
``Matrix-free Neural Preconditioner for the Dirac Operator in Lattice Gauge Theory, [arXiv:2509.10378 [hep-lat]].

Speaker: Ananth Ashish Garg Balasubramanian (Indian Institute of Science)

146 Simulating Supersymmetric Quantum Mechanics Using Variational Quantum Algorithms

The sign problem is a major obstacle for lattice studies of spontaneous supersymmetry breaking (SSB). Quantum computing provides a promising alternative approach. In particular, properties of supersymmetry relate SSB to the ground-state energy, which can be probed using hybrid quantum-classical algorithms such as the variational quantum eigensolver (VQE). I will present VQE analyses for supersymmetric quantum mechanics with various superpotentials. A key new feature is an adaptive ansatz construction algorithm that reduces the number of variational parameters within our ansätze. This lowers the resource burden on both the classical optimizer and the noisy quantum processor, thereby improving the feasibility of these calculations in the NISQ era.

Speaker: John Kerfoot (University of Liverpool)

Lattice2025_Poster_Johnkerfoot.pdf

147 Staggered fermions with taste splitting mass term on dynamical configurations

We present numerical results of staggered fermions with a
taste splitting mass term on dynamical configurations. The rise of gluonic counterterms from rotational symmetry breaking is studied for a single taste operator and the pion propagator is computed. Preliminary numerical results are given for lattice sizes up to $16^4$

Speaker: Nuha Chreim (University of Wuppertal)

148 The matrix model of two-color one-flavor QCD: The ultra-strong coupling regime

We use variational methods to numerically study the matrix model for two-color QCD coupled to a single quark (matrix-QCD(_{2,1})) in the ultra-strong Yang--Mills coupling ((g = \infty)). The model's spectrum is divided into superselection sectors characterized by baryon number (B) and spin (J). Our analysis focuses on the sectors (B = 0, 1, 2) and (J = 0, 1), which correspond to mesons, (anti-)diquarks, and (anti-)tetraquarks. For each sector, we examine the ground-state properties in both the chiral and heavy-quark limits, revealing a rich structure of quantum phase transitions (QPTs). We further analyze how the total spin is distributed between the gluonic and quark components, and find that the gluonic contribution is substantial in several sectors. Finally, by introducing a finite baryon chemical potential (\mu), we construct the model's phase diagram and demonstrate that, for sufficiently large (\mu), the ground state can acquire non-zero spin.

Speaker: ARKAJYOTI BANDYOPADHYAY (Indian Institute of Technology, Bhubaneswar)

TIFR_Lattice_MM_2c1f.pdf

149 Thermodynamic Consistency as a Reliability Test for Complex Langevin Simulations

The complex Langevin method (CLM) is a promising tool to address the sign problem in quantum field theories with complex actions. However, it can converge to incorrect results even when simulations appear stable, highlighting the need for robust diagnostics. Existing checks, such as monitoring drift distributions, are useful but indirect. We propose a complementary test based on the configurational temperature, constructed from the gradient and Hessian of the complex action. Unlike drift-based criteria, this estimator directly probes thermodynamic consistency and provides a physically interpretable cross-check of CLM dynamics. Using one-dimensional PT-symmetric models, we show that it reproduces the input temperature with high precision and sensitively detects algorithmic errors, step-size artifacts, and incomplete thermalization. While demonstrated in simple systems, the method extends naturally to higher-dimensional scalar and gauge theories. Since temperature is tied to the bare coupling in many lattice theories, configurational monitoring can also provide an independent check on coupling-dependent observables. Our results indicate that configurational temperature can enhance CLM reliability across a broad range of applications, including lattice QCD at finite density.

Speaker: Anosh Joseph (University of the Witwatersrand)

150 Theta dependence of the deconfining temperature in SU(3) Yang-Mills theory via imaginary theta simulations

We study the theta dependence of the deconfining temperature in SU(3) Yang-Mills theory. Simulation at real theta causes the sign problem, while simulations at imaginary theta are feasible but suffer from topological freezing that becomes severe at large imaginary theta. We mitigate the topological freezing using two-dimensional parallel tempering technique with replica exchanges across simulation parameters. We found that the technique substantially lowers topological-charge autocorrelations and mitigates freezing. In addition, to eliminate the ultraviolet noise, we use the stout smearing method in the update of the gauge fields. We measure the theta dependence of the deconfining temperature in the imaginary theta region, and estimate it in the real theta region by analytic continuation.

Speaker: Mitsuaki Hirasawa (University of Milano-Bicocca)

lattice_2025_MH.pdf

151 Toward Efficient Trotter-Suzuki Schemes for Long-Time Quantum Dynamics

Accurately simulating long-time dynamics of quantum many-body systems—whether in real or imaginary time—is a challenge in both classical and quantum computing due to the accumulation of Trotter errors. While low-order Trotter-Suzuki decompositions are straightforward to implement, their rapidly growing error limits access to long-time observables and ground state properties. I will present a framework for constructing efficient high-order Trotter-Suzuki schemes by identifying their structure and directly optimizing their parameters over a high-dimensional space. This method enables the discovery of new schemes with significantly improved efficiency compared to traditional constructions, such as those by Suzuki and Yoshida. I will demonstrate the effectiveness of these decompositions on the Heisenberg XXZ model, comparing their performance and presenting the newly discovered schemes. Finally, I will discuss ongoing efforts to extend this framework to even higher orders and apply the derived schemes to quantum hardware, pushing the boundaries of both theoretical advancements and practical quantum computing.

Speaker: Marko Maležič (University of Bonn / Helmholtz Institute for Radiation and Nuclear Physics)

152 Towards continuum estimate of cumulants of conserved charges for (2+1)-flavor QCD with Mobius Domain Wall fermions

We present recent progress towards continuum estimates of cumulants of conserved charges in (2+1)-flavor QCD with Möbius Domain Wall fermions (MDWF). Simulations are performed at the physical quark-mass point on lattices with temporal extent $N_\tau=12,16$ and aspect ratio $N_{\sigma}/N_{\tau}=3$, enabling a controlled study of cutoff effects. We focus on second- and fourth-order cumulants of net-baryon number, electric charge, and strangeness, which provide key inputs for comparisons with heavy-ion collision experiments.

Speaker: Jishnu Goswami (Bielefeld University)

153 Validating a novel approach to the two-dimensional Ising model phase transition

The Ising model serves as a model for simple magnetic systems and as a testing ground for the study of strongly-coupled systems. The model is exactly solvable in two dimensions and can be simulated with relatively small computing resources. We investigate the phase transition of the Ising model through a novel scaling procedure first proposed to explore the phase structure of a theory with four SU(2) doublet fermions in Butt et al. (PRL 134, 2025, 031602). We present a preliminary validation of this scaling procedure by demonstrating that the procedure aligns with the known properties of the two-dimensional Ising model.

Speaker: Christopher Monahan

Monahan_poster_Lattice2025.pdf

154 Variance reduction with normalizing flows

Normalizing flows provide a framework to learn statistically exact machine-learned maps between different lattice field theories. Flows constructed to map from QCD to the same theory with a (possibly localized) operator insertion provide a general tool to construct unbiased reduced-variance estimators for lattice QCD correlation functions. Building on previous applications to Feynman-Hellmann calculations, we extend this approach to include improved computations of two-point and three-point functions. We present preliminary results of several applications of this approach.

Speakers: Daniel Hackett, Gurtej Kanwar (University of Edinburgh)

Dinner

Wednesday 5 November

Algorithms and artificial intelligence

Convener: Ho Hsiao (Center for Computational Sciences, University of Tsukuba)

155 False vacuum decay and a new sampling method for rare events

We present a new Monte Carlo sampling method to calculate the rate at which probability flows out of a meta-stable regime in a complex system. In field theory, this method could be used to calculate false vacuum decay rates. The original probability distribution of the system is multiplied by a simple re-weighting function which guarantees that the system transitions between the meta-stable and stable regimes within a specified range of time. We then perform series of subset simulations with the re-weighting function gradually removed. By combining the results of these simulations, we get the change in the transition probability during the specified time range. Because the re-weighting function is known from the beginning, all simulations can be performed in parallel, or even combined into a single Monte Carlo simulation.

Speaker: Joshua Swaim (University of Connecticut)

156 Simulating Correlated Electrons with Symmetry-Enforced Normalizing Flows

We demonstrate, for the first time, that normalizing flows can accurately learn the Boltzmann distribution of the fermionic Hubbard model—a central framework for understanding the electronic structure of graphene and related materials. Conventional approaches such as Hybrid Monte Carlo often encounter ergodicity breakdowns near the time-continuum limit, introducing systematic biases. By incorporating symmetry-aware architectures and enabling independent, identically distributed sampling, our method overcomes these limitations and delivers substantial performance gains over state-of-the-art techniques.

Speaker: Dominic Schuh (University of Bonn)

157 Towards Scalable Normalizing Flows for the Hubbard Model

Normalizing flows have recently demonstrated the ability to learn the Boltzmann distribution of the Hubbard model, opening new avenues for generative modeling in condensed matter physics. In this work, we investigate the steps required to extend such simulations to larger lattice sizes and lower temperatures, with a focus on enhancing stability and efficiency. We further present the scaling behavior of stochastic normalizing flows for this fermionic system.

Speaker: Janik Kreit (University of Bonn)

158 Normalizing Flows for the Density of States in Abelian Lattice Gauge Theory with a $\theta$-term

A while ago, the generalised density-of-states method was proposed to address the sign problem that arises in systems with a complex action. More recently, with the advent of normalising flows and their ability to model complicated target densities, a flow-based density-of-states approach was developed. This method has been shown to successfully reconstruct the partition function of 0D, 1D, and (1+1)D scalar field theories, recovering the correct Lee–Yang zeros. In this talk, we extend this idea by applying gauge-equivariant normalising flows to reconstruct the density of states in pure (1+1)D U(1) gauge theory with a $\theta$-term. In particular, we focus on the steps required to probe the topological phase transition expected at $\theta = \pi$.

Speaker: Simran Singh (HISKP, University of Bonn)

QCD at nonzero temperature and density

159 Understanding dimensional reduction in finite temperature QCD from spatial string tension and its consequences

We study some of the outstanding non-perturbative properties of QCD at finite temperature $T$ due to the magnetic gluons whose momenta are $|\vec{p}|\leq g^2T/\pi$, where $g$ is strong coupling strength. By performing lattice computations of the spatial Wilson line correlators for a wide range of temperatures from $160$-$1000$ MeV on different lattice spacings corresponding to $N_\tau=8, 12, 16$ for pure SU(3) gauge theory and $N_\tau=8, 10$ for 2+1 flavor QCD we extract the spatial string tension. From the temperature dependence of the spatial string tension we show that QCD can be described by a dimensional reduced effective theory, EQCD, at temperatures beyond $700$ MeV. We further extract the pseudo-potential whose long distance properties are characterized by the spatial string tension and the short distance perturbative part is described within EQCD. We demonstrate how this potential can explain the deviation of the pseudo-scalar and vector screening masses from their perturbative estimates at temperatures as high as $100$ GeV. We also derive the spin-spin interaction potential within EQCD and demonstrate how well it can explain the mass splitting between pseudo-scalar and vector screening masses at high temperatures.

Speaker: Sayantan Sharma (IMSc)

160 Spatial string tension at high temperatures and quantitative tests of dimensionally reduced effective theories

We calculate spatial string tension in 2+1 flavour QCD in (3,1)
dimensions within temperature range of [166MeV, 1000MeV] using spatial
Wilson Loops with HYP smearing. We used Highly Improved Staggered Quark
action for
fermions and tree level Symanzik improved gauge action for gluons at two
lattice spacings corresponding to temporal extent $N_{\tau}=8,10$. We
then compare our results with dimensionally reduced effective theories
at high temperatures ( EQCD and MQCD) to test the onset of dimensional
reduction in QCD.

Speaker: Vishal Rao (Indian Institute of Science, Bangalore)

161 Hadronic screening masses in thermal QCD up to the electroweak scale

Novel theoretical and computational strategies have opened the possibility of exploring QCD thermodynamics at the non-perturbative level at unprecedented temperatures, reaching from the GeV scale up to the electroweak scale.
A number of observable quantities are now being investigated in this regime.
Key ones are the hadronic screening masses, which encode the correlation length of the medium and thus the extent to which strong interactions are screened in a thermal environment.
In this talk I present recent lattice results for hadronic screening masses, including baryonic modes and (preliminary) non-static mesonic modes.
These results can be compared with predictions from the perturbative expansion in the three-dimensional effective theory valid at asymptotically large temperatures.
The comparison reveals persistent non-perturbative effects well into the electroweak scale, shedding new light on the microscopic structure of QCD at extreme temperatures.

Speaker: Marco Cè (Università di Milano-Bicocca)

162 Topological String Configurations in Finite-Temperature SU(3) Gauge Theory

We study Z$_3$ topological string defects in the deconfined phase of pure SU(3) gauge theory via lattice Monte Carlo simulations. These defects occur at the junctions of center domains, where the Polyakov loop winds nontrivially around spatial loops. We determine the string free energy from the action difference between ensembles with and without the defect on $60 \times 60 \times 4$ lattices ($N_\tau = 2$). The results show that the string energy is dominated by attached center-domain walls. Near $T_c$ the string tension $\sigma/T^2$ rises sharply, while at larger $\beta$ it grows linearly. The extracted interface tensions agree with previous lattice determinations, validating the approach. Our results demonstrate that topological strings provide a useful probe of nonperturbative interface dynamics in hot SU(3) gauge theory.

Speaker: Sumit Shaw (IMSc)

Quark and lepton flavor physics

Convener: Steven Gottlieb (Indiana University)

163 f_K/f_{\pi} in isoQCD and the CKM matrix unitarity

We present results for $f_K/f_{\pi}$ in pure QCD with $N_f=2+1$ flavors, along with a determination of $|V_{us}|$ and a study on the unitarity of the first row of the Cabibbo-Kobayashi-Maskawa (CKM) matrix after introducing strong isospin-breaking and QED effects.

The results obtained are based on a combination of a Wilson unitary action and a mixed action setup using Wilson twisted mass fermions in the valence. In both setups, the sea sector employs non-perturbatively $\mathcal{O}(a)$-improved Wilson fermions, using CLS $N_f=2+1$ ensembles.

The combination of the two regularizations enables a more precise control over the continuum limit extrapolation, as both setups must share the same continuum limit, yet can exhibit distinct cutoff effects.

Speaker: Alejandro Saez Gonzalvo (IFIC UV-CSIC)

164 Isospin-breaking contributions to \varepsilon’ from lattice QCD

The precision of current lattice QCD calculations of the direct CP-violating parameter $\varepsilon’$ now requires the inclusion of $\Delta I = \frac{1}{2}$ rule-enhanced, isospin-breaking effects. Here we give an update on the program to include electromagnetism and quark mass differences in a first-principles calculation of $\varepsilon’$. We combine finite-volume hadronic matrix elements with an infinite-volume photon propagator. In order to avoid large finite-volume effects due to low-energy $\pi\pi\gamma$ states, we omit low-energy photons but show this introduces a negligible error. Finally, we discuss technical details related to the mixing of the I = 0 and I = 2 decay channels and the GEVP.

Speaker: Erik Lundstrum (Columbia University)

165 Kaon leptonic and semileptonic decays with N_f=2+1+1 HISQ fermions

Current precision tests of the Standard Model (SM) show a deficit in the first row unitarity of the CKM matrix. At the current level of precision, the only relevant CKM matrix elements that contribute to first row unitarity are $|V_{ud}|$ and $|V_{us}|$. Without resorting on nuclear inputs, those can be extracted from the experimental decay width of kaon and pion leptonic decays along with the theoretical calculation of their decay constants, and semileptonic kaon decays along with the corresponding form factor at zero momentum transfer. In this talk we will discuss progress towards a correlated analysis of the lattice inputs needed for this test using highly improved staggered quarks (HISQ) on the MILC $N_f=2+1+1$ configurations.

We will present the status of a new analysis of light-meson decay constant data where chiral-continuum fits are guided by Staggered Chiral Perturbation Theory (SChPT). The goal of SChPT is twofold: it allows us to use not only physical pion mass data but also unphysical data; moreover, it will also provide values of ChPT Low Energy Constants (LECs) as well as their correlations. We will also present a reanalysis of our previous kaon semileptonic form factor calculation, aiming to estimate correlations between the form factor and light-meson decay constants. We will discuss the new methodology, new data included, and we will also present some preliminary results.

Speaker: Ramón Merino (Universidad de Granada)

166 First-principle evaluation of inclusive hadronic $\tau$ decays in QCD+QED

Hadronic decays of the $\tau$ lepton provide an independent avenue for determining the CKM matrix elements $V_{us}$ and $V_{ud}$. This is particularly relevant given the persistent tensions with CKM unitarity observed when these elements are extracted from leptonic and semileptonic decays of light mesons, as well as from nuclear beta decays. A recent lattice QCD calculation by the ETM Collaboration of the inclusive hadronic $\tau$ decay rate, performed in the isospin-symmetric limit using the HLT method to reconstruct the underlying spectral density, yields $|V_{us}| = 0.2189(7)_\text{th}(18)_\text{exp}$. This result is consistent with a determination based on the operator product expansion but reveals a $3\sigma$ tension with CKM unitarity. To properly assess this discrepancy, it is essential to include electromagnetic and strong isospin-breaking corrections, which are currently neglected in the isospin-symmetric calculation. In this talk, I will present ongoing efforts and future prospects for computing these corrections using both the perturbative RM123 approach and fully dynamical QCD+QED simulations. I will also discuss how such corrections to the decay rate can be extracted from Euclidean lattice correlators through spectral reconstruction techniques, with proper treatment of the correlator renormalisation. The application of the HLT method to these isospin-breaking effects paves the way for future studies of radiative corrections in a broader class of weak decay processes.

Speaker: Matteo Di Carlo (CERN)

Standard Model parameters

Convener: Oliver Witzel (Universität Siegen)

167 RG running and mixing for $\Delta$F = 2 Four-Fermion Operators from Step-Scaling Matrices in $\chi$SF schemes

We show preliminary results for the nonperturbative Renormalization Group (RG) running of the full $\Delta F=2$ four-fermion operators basis in QCD with $N_f=3$ massless dynamical flavours. The perturbative part of the running is obtained extending the conventional approaches in the literature, employing the Poincaré–Dulac theorem. The nonperturbative computations employ $\mathcal{O}(a)$-improved Wilson fermions in a mixed action framework: chirally rotated Schrödinger functional ($\chi$SF) boundary conditions for valence quarks and standard Schrödinger Functional (SF) boundaries for the sea quarks. The RG evolution operators are determined through matrix step-scaling functions (SSF), using a SF coupling in the perturbative regime down to ~4GeV, and a Gradient Flow (GF) coupling from ~4GeV down to ~200 MeV. Moreover, the results have been obtained in two different normalization schemes and validated through a variety of consistency checks.

Speaker: Riccardo Marinelli (“Sapienza” University of Rome)

168 Discretization effects in pure gauge theory

The approach to the continuum of a given discretization of a quantum field theory is understood within the framework of Symanzik Effective Field Theory. It explains the concept of universality whereby dimensionless renormalized observables approach the same continuum value in any discretization. The functional form of these observables as functions of the lattice spacing depends on the anomalous dimensions of the involved operators and can be quite complicated. In order to state precision results in lattice field theory, we claim it is crucial to assure oneself that universality holds and that the simulation is performed in a parameter region where the continuum approach is asymptotic. Using quantities derived from the gradient flow, we perform such a test in pure gauge theory. In this talk, we report on the results from this study and demonstrate, how one can easily draw incorrect conclusions from flow-time ratios and propose a more careful method.

Speaker: Nicolas Lang (IFIC, U. Valencia and CSIC)

169 Light and strange quark masses with $N_f=2+1$ Wilson fermions

We report on the status of an update of our previous computation of light and strange quark masses in QCD with $N_f=2+1$ dynamical flavour. Bare quark masses are extracted from CLS ensembles, using $\mbox{O}(a)$-improved Wilson fermions, and the mass renormalization is performed non-perturbatively in the Schrödinger functional scheme over a wide range of scales to make safe contact with perturbation theory. Results for five lattice spacings, down to $a \approx 0.038 \,\mathrm{fm}$, and pion masses reaching the physical value are included in the analysis. This allows for the exploration of different models for cutoff and chiral effects, and a controlled extrapolation to the physical point.

Speaker: Fernando Pérez Panadero (IFT-UAM/CSIC)

170 Heavy quark masses from step-scaling

We present a determination of the charm- and bottom-quark masses using the step-scaling approach to heavy-quark physics. Renormalization is performed in small volumes where relativistic bottom quarks can be simulated directly. A sequence of finite-volume simulations connects this calculation to large-volume CLS ensembles, where simulations at physical light and strange quark masses provide reliable control over low-energy hadronic physics. In all but the smallest volume, the B-scale is reached by interpolating between relativistic heavy-quark data and the static limit. The resulting quark masses are obtained with good precision, with subdominant systematic uncertainties that differ from, and thus complement, those of standard large-volume determinations.

Speaker: Simon Kuberski

Structure of hadrons and nuclei

Convener: Marcel Rodekamp (Universität Regensburg)

171 Electric Polarizability of Charged Pions from nHYP Four-Point Functions

Understanding a hadron’s electric and magnetic polarizabilities allows one to access internal structural information. Traditionally, the external field two-point function method has been used to calculate polarizabilities. However, recent work has demonstrated the effectiveness of using four-point functions for computing polarizabilities of charged and neutral hadrons. Our previous study on the electric polarizability of the charged pion used a quenched Wilson action on a lattice with pion mass from 1100 MeV to 370 MeV. In this work, we employ a number of improvements, including a dynamical action (nHYP), smaller pion masses, and a variable lattice size in order to extrapolate to infinite volume. I will describe the analysis procedure, some early results, and expectations for future work.

Speaker: Benjamin Luke (Baylor University)

172 Probing Instanton Dynamics in the Pion Vector Form Factor with Wilson Flow

Instanton liquid model is believed to capture the main features of vacuum QCD dynamics. Recently, multiple predictions for hadron structure functions have been derived and compared with experimental measurements and lattice QCD calculations, finding a general agreement. In order to explore the precision of the instanton liquid model, one has to compare its predictions with non-perturbative simulations in a regime dominated by instanton dynamics.
This has been performed for two gluon-sensitive observables: the gluon Green's function and the strong running coupling constant [1]. In this contribution, we propose to study a fermionic observable, the pion vector form factor, for which instanton liquid model predictions have been discussed in [1]. We use the Wilson flow to single out the dominant contribution from the instantons out of a lattice QCD configuration ensemble. We describe the details of our numerical setup, and some first, preliminary results.

References:

1. Wei-Yang Liu, Edward Shuryak, and Ismail Zahed, Phys. Rev. D 109,
   074029 (2024). doi:10.1103/PhysRevD.109.074029

Speaker: Vaibhav Chahar (Jagiellonian University, Poland)

173 The Electromagnetic Form Factor of the Rho Meson on the Lattice

The calculation of the hadronic form factors on the lattice provides important information about the internal structure of the corresponding states. However, calculating the form factor for unstable states, viz. resonances, is not as straightforward, both from the conceptual point of view and in terms of technical implementation. In this work, we specifically consider the electromagnetic form factor of the $\rho$-meson. It is well known that the matrix element of the current between two eigenstates of the lattice Hamiltonian with energies close to the resonance mass does not possess a well-defined infinite-volume limit, even if the Lellouch-Lüscher factors for the external legs are properly taken into account. The reason for this is that the triangle diagram, where the external current is hooked on to one of the constituents of the resonance, does not exhibit a regular dependence on the box size.

In this work, we make use of the external field method (the Feynman-Hellmann method), where the system is placed in an external field, coupling to a spatially periodic current. The structure of the finite-volume energy levels is described by the modified Lüscher equation, which enables one to directly extract the short-range part of the interaction with the external field from the fit to the shifted energy levels. This method has the advantage that the separation of the triangle diagram is automatically taken into account, and the short-range interaction has a regular dependence on L, which is exponentially suppressed for large L. Through this work, we provide complete framework for the extraction of the form factor from raw lattice data, when available. We, in addition, provide a crude estimate of the short-range contribution to the form factor at the lowest order in ChPT.

Speaker: Ajay Shanmuga Sakthivasan (HISKP, University of Bonn)

Theoretical developments and applications beyond Standard Model

Convener: Anosh Joseph (University of the Witwatersrand)

174 Tensor renormalization group approach to critical phenomena via twisted partition functions

We show that the tensor renormalization group offers a consistent framework in which twisted partition functions can be employed as order parameters to study critical phenomena. Investigating the two-dimensional Ising model and the three-dimensional $O(2)$ model as concrete examples, we demonstrate that critical points associated with spontaneous symmetry breaking can be located solely from the twisted partition functions. We further apply our method to the two-dimensional $O(2)$ model and show that the helicity modulus can be directly extracted from the twisted partition functions.

Speaker: Shinichiro Akiyama (University of Tsukuba)

175 Tensor Network approach to Entanglement Entropy and Critical Point in (1+1)D Real Scalar phi^4 Theory

We present the entanglement entropy for the two-dimensional real scalar φ^4 theory using a higher-order tensor renormalization group algorithm. This quantity is employed to identify a critical point of the system. We will also discuss the continuum limit of the critical point.

Speaker: Mr Takahiro Hayazaki (Kanazawa University)

176 Analysis of Finite Density 3d Complex Scalar Theory by MDTRG

Tensor Renormalization Group (TRG) is a promising numerical
method for systems with the sign problem. However, the computational
cost increases exponentially with the dimension, which makes the
development of effective algorithms for three-dimensional or
four-dimensional models a crucial challenge. As a first step toward
addressing this, we study the three-dimensional finite-density complex
scalar model using the MDTRG, which has been proposed as an efficient
algorithm. This model possesses the Silver Blaze phenomenon, which also
occurs in low-temperature, finite-density QCD. We determine the critical
chemical potential from computations of particle number density and
scalar field expectation values, as well as demonstrate that the MDTRG
efficiently works for systems in three-dimensional field theory.

Speaker: Hayato Aizawa (Kanazawa University)

177 The study of multi-particle states with the tensor renormalization group method

We develop a computational scheme based on the tensor renormalization group method to investigate the multi-particle state of the (1+1)d Ising model. The scheme is started by representing the system as a tensor network and coarse-graining it with the higher-order tensor renormalization group algorithm. Thereafter, we construct the corresponding numerical transfer matrix from the coarse-grained tensor and evaluate its eigenvalues to extract the energy spectrum. Following this, we classify the quantum number of the energy eigenstates by computing the matrix elements of a proper insertion operator. The matrix elements are represented as impurity tensor networks and computed with the coarse-graining scheme. After the classification, we identify the number of particles in each eigenstate from the size dependence of the corresponding energy eigenvalues, and we can detect up to the four-particle state. From the two particle-state sectors, we analyze the dynamics by computing the scattering phase shift with two approaches i.e. first is from the energy spectrum with a help of Lüscher’s formula and second is from the two-particle state wave function.

Speaker: Fathiyya Izzatun Az Zahra (Kanazawa University)

10:20 Coffee break

The program ends for the day. Lunch boxes will be distributed to the participants.

Algorithms and artificial intelligence

Convener: Johann Ostmeyer (University of Bonn)

178 Critical behavior of the Schwinger model via gauge-invariant variational uniform matrix product states

We study the lattice Schwinger model by combining the variational uniform matrix product state (VUMPS) algorithm with a gauge-invariant matrix product ansatz that locally enforces the Gauss law constraint. Both the continuum and lattice versions of the Schwinger model with $\theta=\pi$ are known to exhibit first-order phase transitions for the values of the fermion mass above a critical value, where a second-order phase transition occurs. Our algorithm enables a precise determination of the critical point in the continuum theory. We further analyze the scaling in the simultaneous critical and continuum limits and confirm that the data collapse aligns with the Ising universality class to remarkable precision.

Speaker: Prof. Takuya Okuda (University of Tokyo)

179 Ground state search of interacting boson–fermion systems using variational Monte Carlo

This work is motivated by the limitations of conventional Euclidean Monte Carlo methods, particularly the sign problem, which hinder the exploration of physically rich regimes such as nonzero chemical potential, topological terms, and real time dynamics. To address this challenge, we present a Hamiltonian-based variational approach for numerical simulations of quantum mechanical systems. We benchmark our method on two physical models of interest—2+1D compact lattice QED with Wilson fermion discretization, and the minimal BMN matrix model.

We employ a variational Monte Carlo algorithm, where we construct a parameterized ansatz state and approximate the ground state by minimizing the energy w.r.t. the variational parameters. The ansatz is decomposed into two parts—a gauge/bosonic part and a fermionic part, each constructed using gauge invariant combinations of the underlying degrees of freedom. For the gauge/bosonic part of the ansatz, we work in a continuous basis of the physical Hilbert space to avoid basis truncations (such as cutoffs in electric flux or bosonic occupation numbers, which are introduced to make the infinite-dimensional degrees of freedom numerically tractable). The expectation values are computed in this continuous basis by numerical integration using Monte Carlo. To avoid the fermionic sign problem we approximate the fermionic part of the ansatz as a fermionic gaussian state for each gauge/bosonic field configuration. As a result, the expectation value w.r.t. to fermionic state is computed analytically, removing the need for sampling from fermionic distributions.

We show preliminary results for the ground state preparation in the sign problem afflicted regimes of the 2+1D compact lattice QED and the BMN matrix model, demonstrating the viability of this Hamiltonian variational approach and offers a path towards studying regimes inaccessible to Euclidean Monte Carlo.

Speaker: Pranay Naredi (DESY, The Cyprus Institute)

180 All-mode technique for higher-order tensor renormalization group in two and three dimension

We introduce an all-mode extension of the Higher-Order Tensor Renormalization Group (HOTRG) by using a squeezer transformation at the coarse-graining step. This all-mode framework eliminates systematic errors, leaving only statistical uncertainties, enabling direct comparison with exact results. We demonstrate the method on the two- and three-dimensional Ising models, obtaining results in agreement with exact solutions.

Speaker: Katsumasa Nakayama (RIKEN)

Hadronic and nuclear spectrum and interactions

Convener: Srijit Paul

181 Electromagnetic form factors and structure of the $T_{bb}$ tetraquark

We present the first lattice QCD determination of the electromagnetic form factors of the exotic tetraquark $T_{bb}$ ($bb \bar u \bar d$) with quantum numbers $I( J^P ) = 0( 1^+ )$. The extracted form factors encode information about its internal structure, including the charge distribution and the magnetic dipole moments, determined separately for the light and heavy quarks. Our results provide evidence in favor of it being a bound state consisting of a compact heavy diquark $[bb]$ in a color-antitriplet with spin one, and a light antidiquark $[\bar u \bar d]$ in a color-triplet with spin zero. The charge radius of $T_{bb}$ is found to be significantly smaller than the combined charge radii of $B$ and $B^*$ mesons. These two comprise the lowest-lying threshold $BB^*$ in the channel we are considering, and their electric charge form factors are also determined. The computations were done on a single CLS ensemble with $N_f = 2+1$ dynamic quarks and a spacing of approximately $a \approx0.064 \ \mathrm{fm}$ at the pion mass $m_\pi \approx 290 \ \mathrm{MeV}$.

Speaker: Ivan Vujmilovic

182 Born--Oppenheimer Effective Theory for multiquark states

The discovery of XYZ exotic states in the hadronic sector, particularly those containing two heavy quarks, remains one of the most intriguing open problems in particle physics. In this talk, I present the Born-Oppenheimer Effective Field Theory (BOEFT), a framework derived from QCD, capable of describing exotic hadrons of any composition. I present results on the key nonperturbative gauge-invariant correlators to be computed on lattice QCD—such as static energies, generalized Wilson loops, gluelumps, and adjoint mesons—for understanding the patterns of XYZ states. Moreover, I show for the first time new results on the behavior of static energies at short distances and mixing with the threshold at long distances based on BOEFT. As an application, I show results for the hybrid spectrum, hybrid decays to quarkonium, results for X(3872) and T_cc (3875), and pentaquark states.

Speaker: Abhishek Mohapatra (Technical University of Munich)

183 Adjoint meson and tetraquark static energies using novel BOEFT interpolators

We aim to explore the $Z_b$ tetraquark channel, $\bar{b}b\bar{d}u$, with quantum numbers $J^{PC}=1^{+-}$. Our approach involves calculating correlators among three operator classes: (i) static-light pair, (ii) quarkonium plus pions, and (iii) the novel interpolator based on BOEFT (Born–Oppenheimer Effective Field Theory) proposed in Ref. [1]. We use the GEVP variational approach to extract the preliminary eigenenergies and overlap factors from the correlation matrix. At short distances, at leading order, this novel interpolator has zero overlap with quarkonium and pions due to the $Q\bar{Q}$ pair being in a color-octet configuration, whereas at large distances it conveniently evolves into a heavy-light pair, making it a suitable choice to calculate the tetraquark static energies on the lattice. To achieve this, we employ the distillation technique on a CLS ensemble with $N_f=2+1$ and $m_{\pi}=290$ MeV.

In the limit of zero spatial separation between the static quark and antiquark, the diagonal correlator associated with the novel interpolator reduces to the correlator of an adjoint meson, i.e., a state composed of a static adjoint source bound to a light quark–antiquark pair. We will present the preliminary spectrum of the corresponding $I=1$ adjoint mesons in the scalar, pseudoscalar, and vector channels. For this, we use $N_f=3+1$ ensembles produced with the openQCD package [2], with $m_{\pi}=406$ MeV, $N_{\sigma}=32$, and $N_\tau=96$, with open boundary conditions in time.

[1] Matthias Berwein, Nora Brambilla, Abhishek Mohapatra, and Antonio Vairo. Hybrids, tetraquarks, pentaquarks, doubly heavy baryons, and quarkonia in Born–Oppenheimer effective theory. Phys. Rev. D 110(9):094040, 2024.

[2] ALPHA Collaboration. Scale setting for $N_f=3+1$ QCD. Eur. Phys. J. C 80 (2020) 349 [2002.02866].

Speaker: Sipaz Sharma (TUM)

QCD at nonzero temperature and density

184 $U(1)_A$ symmetry restoration at finite temperature with mesonic correlators

The $U(1)_A$ symmetry of the massless QCD Lagrangian is broken in the quantised theory but may be effectively restored at some finite temperature with important consequences on the order of the chiral transition and the QCD phase diagram in the chiral limit. It has been argued in the literature that one way to probe the effective restoration of $U(1)_A$ is to check for the degeneracy of flavour non-singlet pseudoscalar and scalar correlators. In this work, we consider a new method of examining this degeneracy based upon hadron correlation functions on the anisotropic FASTSUM ensembles. The anisotropic nature and our newest Generation 3 ensemble aid in a precise determination of the effective restoration of the $U(1)_A$ symmetry which we find to be $T_{\text{chiral}} <T_{U(1)_A}\lesssim 2\,T_{\text{chiral}}$ at finite quark mass.

Speaker: Ryan Bignell (Trinity College Dublin)

185 Understanding properties of the Dirac eigenspectrum in QCD and approach to thermalization

In this work, we calculate the eigenvalues of the probe (overlap) Dirac operator on thermal gauge ensembles of 2+1 flavor QCD generated using domain wall fermions as well as pure SU(3) gauge theory on the lattice. Focusing on the infrared part of the eigenspectrum that lies within the non-perturbative magnetic scale, we propose suitable observables that allow us to categorize different regions of the eigenspectrum unambiguously. While most of these eigenmodes are completely delocalized and chaotic, i.e. their nearest-neighbor level spacing fluctuations are similar to random matrices of a Gaussian unitary ensemble, we showed that a classical non-thermal state of SU(3) gauge theory consisting of magnetic gluons is also chaotic, thus a non-trivial realization of the Bohigas-Giannoni-Schmit conjecture. This allowed us to estimate an upper bound on the thermalization time $\sim 1.44$ fm/c of magnetic gluons by matching the magnetic scales in these two regimes. Furthermore we also observe the appearance of a few eigenmodes in deep-infrared part of the spectrum near and above the chiral crossover temperature, whose fractal dimensions might carry information about the universality class of the chiral transition in QCD.

Speaker: RAVI SHANKER (The Institute of Mathematical Sciences)

186 Topological susceptibility with 2+1 flavor Moebius domain wall fermion at finite temperature

The topological susceptibility is one of the quantities that has a large discretization error, and the error can be sensitive to the choice of fermion action. We report on our results from physical point simulations with 2+1 flavor Moebius domain wall fermion at finite temperature. The temporal lattice size is Nt=12 and 16, and the temperature range is around 140 MeV to 250 MeV. We also present results on ensembles with 1/a ~ 2.5 GeV of which quark mass is slightly off from the physical point.

Speaker: Issaku Kanamori (R-CCS, RIKEN)

Quark and lepton flavor physics

Convener: Andrew Lytle

187 Nevanlinna-Pick interpolation from inexact data

First-principles prediction of inclusive heavy-particle decay is key to interpreting experimental data and testing the Standard Model. However, lattice QCD data requires ill-posed analytic continuation before such predictions can be made. Bergamaschi, et al. proposed using Nevanlinna-Pick interpolation to address this inverse problem which provides rigorous bounds on the continued results. We propose a precise method to incorporate the uncertainty inherent in lattice data in this interpolation. The combined lattice and interpolation errors for the simplified example studied are statistically well-controlled and suggest that ab initio lattice methods may be applied to these inclusive processes.

Speaker: Sarah Fields (Columbia University)

188 Non-perturbative Weak Physics using the FMS Mechanism

The SU(2) gauge symmetry of the weak sector implies that the Higgs vacuum expectation value has to be gauge variant and hence cannot be a physical observable, even though it is generally regarded as such. The standard perturbative expansion, therefore, has a conceptual flaw that can be resolved using the Fröhlich-Morchio-Strocchi mechanism. In this presentation, we explore the mechanism on the lattice. We will present new results for Higgs and W-boson PDFs from quenched simulations. Further, we present results from simulations with dynamical fermions, identifying different physical regions that exhibit QCD-like and Higgs-like mass hierarchies, where the Higgs is either stable or a resonance. We discuss the operator basis developed to produce lepton scattering lengths from a Lüscher analysis, as well as preliminary spectral functions and extracted scattering amplitudes obtained in the different physical regions.

Speaker: Sofie Martins (University of Graz)

189 Electromagnetic pion mass splitting using PV-regulated photon propagator

Many hadronic observables are nowadays computed in lattice QCD with a sub-percent precision which requires the inclusion of isospin-breaking and electromagnetic effects. Most of the methods that implement the photon propagator in finite-volume lead to power-law suppressed finite size effects. These are due to the long-range nature of electromagnetism and make reliable predictions computationally demanding. This issue can be avoided by working with a regulated photon propagator (introducing a Pauli-Villars mass $\Lambda$) directly in continuum and infinite volume. This feature can be profitably exploited to improve the determination of leading-order electromagnetic corrections to several observables such as the HVP or nucleon masses. In this work we test this strategy for the charged/neutral pion mass difference $M_{\pi^+}-M_{\pi^0}$ using CLS $n_f=2+1$ ensembles. We show preliminary results addressing both the dependence on the regulator $\Lambda$ and the chiral-continuum extrapolation with pion masses between 160 and 280 MeV and lattice spacing in the range $[0.049,0.085]$ fm.

Speaker: Alessandro De Santis (Helmholtz-Institut Mainz, Johannes Gutenberg-Universität Mainz)

Structure of hadrons and nuclei

190 Recent update of nucleon axial-vector charge with the PACS10 superfine lattice

We present the results of the nucleon axial-vector charge based on PACS10 gauge ensembles. These ensembles are generated by PACS Collaboration using stout-smeared O(a) improved Wilson-clover quark action and Iwasaki gauge action, and they are characterized by the spatial extent of 10 fm and three lattice spacings 0.09 fm, 0.06 fm and 0.04 fm. In particular, the latest update at 0.04 fm is provided. The PCAC mass is also evaluated from the nucleon three-point functions to verify the axial Ward-Takahashi identity.

Speaker: Masato Nagatsuka (Tohoku University)

191 Updates on the calculation of nucleon matrix elements

We present an update on the Los Alamos collaborations' calculations of the spectrum, charges, form-factors, and electric dipole moments of nucleons using lattice QCD. Our calculations are done using Wilson-Clover fermions on both Clover and MILC collaboration's HISQ gauge configurations. These ensembles include multiple lattice spacings down to 0.04 fm, and multiple isospin-symmetric pion masses below 320 MeV, including some with roughly the physical mass.

Speaker: Tanmoy Bhattacharya (Los Alamos National Laboratory)

192 Precision Scale Setting in Lattice QCD Using Baryon Spectra and Decay Constants

The determination of the lattice scale with high precision is a prerequisite for extracting reliable physical results from lattice QCD. We present an analysis of scale setting using 2+1-flavor Wilson–clover ensembles generated by the JLab/W&M/LANL/MIT/Marseille collaborations with the Hybrid Monte Carlo algorithm. These ensembles span a broad range of lattice spacings ($0.056 \leq a \leq 0.127$ fm), pion masses ($M_\pi \approx $130–270 MeV), and volumes ($3.7 \leq M_\pi L \leq 6.2$), enabling controlled chiral, continuum, and infinite-volume extrapolations.

We use baryon spectra and pseudoscalar decay constants to determine the lattice spacing, assess systematic uncertainties, and cross-validate scale-setting procedures. The analysis includes a study of two-point correlation functions computed with the CHROMA software package, the extraction of masses and decay constants, and a combined fit strategy for extrapolating to the physical point. The resulting precision determination of the lattice scale provides a solid foundation for ongoing and future calculations of hadron structure and matrix elements on these ensembles.

Speaker: Jun-Sik Yoo (Los Alamos National Laboratory)

12:00 Excursions

Thursday 6 November

Plenary session

Convener: Anthony Kennedy

193 Machine learning for lattice gauge theories

I will briefly review how machine learning can be used in lattice gauge theory simulations and what approaches are currently available. I will then dicuss one specific application in more detail, namely the machine learning of RG-improved gauge actions using gauge-equivariant convolutional neural networks. In particular, I will present scaling results for a machine-learned fixed-point action in 4d SU(3) gauge theory towards the continuum limit. The results include observables based on the classically perfect gradient-flow scales, which are free of tree-level lattice artifacts to all orders, and quantities related to the static potential and the deconfinement transition.

Speaker: Urs Wenger (University of Bern)

194 Machines and Exascale computing

I will review the current generation of exascale supercomputers and present performance results for lattice applications. On the software side, I will discuss strategies for achieving performance portability across heterogeneous architectures. I will conclude with an outlook on architectures now under development.

Speaker: Stefan Krieg

10:35 Coffee break

Plenary session

Convener: Robert Mawhinney (Columbia University)

195 Quantum Simulation of Gauge Theories for Particle and Nuclear Physics: Past, Today, and Future

Despite the impressive success of the lattice-gauge-theory program in enabling first-principles predictions in particle, hadronic, and nuclear physics over the years, a range of systems and phenomena will remain out of reach of our current computational paradigm. These include studies of large atomic nuclei and their properties, of phases of matter at finite density, and of the nonequilibrium state of matter and its evolution toward equilibrium in the early universe and in particle colliders. Can a large reliable quantum simulator/computer eventually enable studies of matter governed by the underlying interactions? What does a quantum simulator have to offer to simulate the Standard-Model dynamics, and how far away are we from such a dream? In this talk, I will describe a vision for how we may go on a journey toward quantum simulating the Standard Model and beyond; will motivate the need for novel theoretical, algorithmic, and hardware approaches to quantum simulating this unique problem; and will provide examples of recent progress in using current quantum hardware that demonstrate the potential of this approach in addressing our field-specific problems.

Speaker: Zohreh Davoudi (University of Maryland)

196 Quantum simulation of lattice gauge theories

Gauge theories are the cornerstone of our description of nature. At the theoretical level, many of their fascinating aspects - from real time dynamics, to regimes of finite density of baryon matter - represent some of the most notable and fascinating challenges for computational methods. Over the last decade, this has stimulated a broad effort to understand how to quantum simulate gauge theories with synthetic quantum matter.

In this talk, I will present an overview of the field. After an introduction to quantum computing and simulation, I will discuss why quantum simulating gauge theories is fundamentally different from traditional statistical physics models, explaining conceptual as well as fundamental aspects. I will then review some early proposals on how to use quantum computers and simulations to realize gauge theory dynamics, and contrast them with more recent approaches, including the experimental state of the art. Finally, I will discuss some pressing open problems in this direction, with a specific focus on the relation between gauge theories and fault-tolerant quantum computing.

Speaker: Marcello Dalmonte (ICTP)

197 Panel discussion on Future of Computing

Speaker: Robert Mawhinney (Columbia University)

13:15 Lunch break

Software development and machines

Convener: Mathias Wagner (Nvidia)

198 Yotta

Speaker: Sunil Gupta (Yotta)

199 Sovereign AI Platforms for Research and Innovation: The Shakti Cloud Approach

Recent global events have shown how easily access to critical technologies can be disrupted - whether due to trade restrictions, export controls, or the conflicting obligations of multinational corporations caught between multiple jurisdictions. These developments highlight a profound truth: a nation’s digital future cannot be secure, inclusive, or self-reliant if its foundational technology infrastructure is vulnerable to forces beyond its borders.

This challenge becomes even more urgent in the era of Artificial Intelligence. AI is not only shaping industries, economies, and societies, it is also redefining global power balances. From large language models and scientific simulations to defense and healthcare applications, AI relies on massive computing power. If this capacity resides solely in infrastructure controlled elsewhere, the risks to innovation, data sovereignty, and long-term competitiveness are immense. Building sovereign AI infrastructure is therefore central to ensuring nations maintain control over their digital destiny.

Shakti Cloud is one of India’s advanced sovereign platforms for high-performance computing and artificial intelligence. It is powered by NVIDIA H100 and L40S GPUs (B200 GPUs coming soon) with high-speed interconnects and offers up to 16 exaflops of capacity. It can handle demanding workloads like training state-of-the-art AI models to driving complex scientific research. An important feature of Shakti Cloud is that the entire system is built and operated within India, ensuring that the country’s researchers and enterprises can access world-class infrastructure while retaining control within national boundaries.

For researchers and scientists, access to large-scale computing makes it possible to run experiments, train models, and perform simulations at a speed and scale that was previously difficult within India. Shakti Cloud is designed to support these needs with infrastructure that reduces dependence on external providers. Through Shakti AI Lab, universities and institutes can work with ready-to-use environments that come with widely used tools such as TensorFlow, PyTorch, and Jupyter, lowering the barriers for students and faculty to begin experimenting with AI. For more advanced projects, Shakti Clusters use orchestration systems like Kubernetes and SLURM to help teams manage and scale complex training jobs. To support deployment, Shakti AI Endpoints enable models to run with low latency across different fields, including healthcare, scientific research, media, and industrial applications.

Shakti Cloud also provides serverless GPUs and bare metal as a service, creating a flexible and scalable AI infrastructure. This setup supports diverse applications - from education and research to enterprise and national-level AI projects - while keeping computational resources controlled within India. The platform also considers accessibility and resource allocation, offering flexible usage options that allow startups, academic institutions, and research labs to access high-performance computing without long-term commitments. Overall, Shakti Cloud represents an effort to develop sovereign AI infrastructure within India. By maintaining control over computational resources domestically, it aims to support researchers, students, and the broader scientific community in pursuing AI and HPC work with greater independence and continuity.

Speaker: Vishal Aggarwal (Yotta)

200 NVIDIA

Speaker: Jigara Halani (NVIDIA)

Algorithms and artificial intelligence

Convener: Yusuke Namekawa (Fukuyama University)

201 Bootstrap-determined $p$-values in lattice QCD

We present a method based on the bootstrap to determine $p$-values from Monte Carlo data, in particular those generated in a lattice QCD calculation, where we make no assumptions about the underlying distribution. By generating samples from the underlying data, we are able to naturally incorporate the effects of autocorrelations and non-normally-distributed samples, both of which skew the distribution away from the conventional $\chi^2$ or $t^2$ distributions. Additionally, with these methods we can estimate the p-values for uncorrelated fits and more elaborate fitting procedures for which these analytical distributions are also unsuitable. (This talks summarizes work published in 10.1103/PhysRevD.111.074514)

Speaker: Rajiv Eranki (Columbia University)

202 The Truncated Hankel Correlator Method

A new method to approximate Euclidean correlation functions by exponential sums is introduces. The truncated Hankel correlator (THC) method builds a Hankel matrix from the full correlator data available and truncates the eigenspectrum of said Hankel matrix. It proceeds by applying the Prony generalised eigenvalue method to the thus obtained low-rank approximation. A large number of algebraic correlator analysis methods including (block) Prony (and equivalently (block) Lanczos) and the generalised eigenvalue problem (GEVP) can be reproduced as sub-optimal special cases of the THC method. Moreover, the THC method is robust against noise and requires comparably little human oversight. When applied to symmetric data, the obtained energy spectrum is guaranteed to be symmetric up to machine precision. It goes without saying that the signal-to-noise problem has not been solved.

Speaker: Johann Ostmeyer (University of Bonn)

203 A first study of strong isospin breaking effects in lattice QCD using truncated polynomials

Computing derivatives of observables with respect to parameters of the theory is a powerful tool in lattice QCD, as it allows the study of physical effects not directly accessible in the original Monte Carlo simulation. Prominent examples of this include the impact of the up-down quark mass difference and electromagnetic corrections. In this talk, I will present a new approach based on automatic differentiation to evaluate such derivatives to arbitrarily high orders. Particular emphasis will be placed on strong isospin-breaking effects and on the propagation of derivatives through the conjugate gradient algorithm in the computation of correlation functions. Finally, I will compare the computational cost of this method with that of the RM123 approach and with explicit strong isospin-breaking simulations.

Speaker: David Albandea (Helmholtz-Institut Mainz, GSI)

204 Towards a Renormalization-Group Preconditioned Conjugate Gradient for Domain Wall Fermions

Recent advances such as multigrid and deflation have significantly accelerated Dirac operator solves in lattice QCD. However, the substantial setup costs of these methods have impeded their application in the repeated Dirac inversions required for HMC ensemble generation. Building on earlier work at Columbia University, which showed that renormalization-group (RG) blocked coarse lattices with $a^{-1} = 1$ GeV provide a good approximation of the low-mode structure of Mobius domain wall fermion (MDWF) Dirac operators on $a^{-1} = 2$ GeV lattices, we investigate how to exploit this correspondence in practice. Specifically, we study how filters and Wilson flow on the coarse lattices can be used to control the influence of higher modes in the coarse-fine mapping. Because RG blocking is computationally inexpensive, this approach could provide a way to incorporate multigrid-style acceleration directly into ensemble generation.

Speaker: Jonah Eick (Columbia University)

205 Configurational Thermometer for Lattice Gauge Theories.

We present a new temperature estimator for lattice gauge theories. This estimator is based on the gradient and Hessian of the Euclidean action. It draws inspiration from geometric methods in statistical mechanics. This approach provides a gauge-invariant and momentum-free way to check thermodynamic consistency in Monte Carlo simulations. Unlike traditional methods, which control temperature indirectly by adjusting lattice size or coupling, our estimator finds the effective temperature directly from field configurations. This allows for independent checks of thermalization and sampling accuracy. We apply the estimator to compact U(1) lattice gauge theories in one, two, and four dimensions. We compare the measured temperatures with the input temperatures over a wide range of couplings and lattice sizes. The estimator reliably reproduces the target temperature and performs well against discretization effects and algorithmic artifacts. It can spot sampling issues, slow thermalization, or errors in implementation, making it a useful tool for large-scale simulations. We also discuss potential extensions to non-Abelian theories, anisotropic lattices, and integration with hybrid Monte Carlo workflows.

Speaker: Vamika Longia (Indian Institute of Science Education and Research, Mohali)

206 Diagonal Kenney-Laub Rational Approximation to the Overlap Dirac Operator

Preliminary results are presented for an implementation of the overlap Dirac operator in lattice QCD based on the diagonal Kenney-Laub (KL) rational approximation to the matrix sign function. Both the Wilson and Brillouin Dirac operators are tested as kernels. As in any other rational approximation, the diagonal KL iterates of order (n,n) can be decomposed into partial fractions with n poles, which are inverted using a multi-shift conjugate gradient solver. This representation requires no spectral information, simplifying the implementation. We compute the PCAC quark mass and pion mass and determine the critical bare mass for several n, confirming that the additive mass shift and the violation of the Ginsparg–Wilson relation decrease monotonically with n. We also compare the Wilson and Brillouin kernels and find favorable performance for the latter in terms of CPU time.

Speaker: Mr Stylianos Gregoriou (The Cyprus Institute)

Hadronic and nuclear spectrum and interactions

Convener: Jeremy Green (DESY, Zeuthen)

207 Lattice QCD study on kaon-nucleon interactions and $\Theta^+$ pentaquark on the physical point

Interactions between a meson and a nucleon play an important role in a variety of phenomena such as the partial restoration of chiral symmetry and the structure of exotic hadrons and nuclei. Although kaon-nucleon scattering experiments have been performed since the 1960s, our understanding of the interactions remains limited due to a lack of experimental data at low momenta, making it difficult to accurately elucidate the related physics. On the other hand, recent developments in computational power and lattice QCD techniques have enabled a precise determination of hadron interactions from first principles. In this study, we investigate the S-wave kaon-nucleon interactions in lattice QCD using the time-dependent HAL QCD method. The calculation is performed with $N_f=2+1$ quark flavors at the physical point, $m_{\pi}\approx 137$ MeV, using the configurations generated by HAL QCD Collaboration, “HAL-conf-2023”.
The resulting interaction potential exhibits a purely repulsive behavior for isospin $I=1$, while for $I=0$ a slight attractive pocket is observed in addition to repulsion. The obtained scattering observables are qualitatively consistent with the experimental results. Particularly, our results suggest the P-wave dominance at low momentum for $I=0$. Furthermore, our results indicate that there are no bound or resonant states corresponding to the $\Theta^{+}$ pentaquark in this system.

Speaker: Kotaro Murakami

208 The $\Lambda(1405)$ at the $SU(3)$ point in lattcice QCD

The pole structure of the $\Lambda(1405)$ has been a topic of debate for a long time. Chiral perturbation theory predicts that its experimental spectrum may be explained by a two pole structure originating in the $SU(3)$ chiral dynamics of the baryon-meson interaction. The $SU(3)$-symmetric flavor point is readily accessible in lattice QCD, in this work we study the baryon-meson states directly at this point. We construct interpolation operators that belong to the irreducible representations of $SU(3)$ that are attractive in the channel with the quantum numbers of the $\Lambda (1405)$ (singlet and two octets). The extracted energy levels can be used as input for chiral perturbation theory to find the poles associated with each representation. The relevant correlation functions are computed on $SU(3)$-symmetric ensembles with $M_\pi \approx 714 MeV $ using the distillation technique.

Speaker: Javier Suarez Sucunza (University Bonn)

209 A curious case of a strangeness resonance -- lattice and experiment

The double-pole structure of the strangeness S=-1 isoscalar baryon resonance has become a poster child for the complicated, non-perturbative structure of QCD at low energies. Traditionally, the most successful theoretical approach to study this state has been based on the extensions of Chiral Perturbation Theory. This remains so far the primary methodology underlying the pole positions quoted by the Particle Data Group.

Recent lattice QCD studies provided a new twist on that matter determining finite-volume spectrum at not too heavy pion mass including piSigma and KbarN channels. The question to be discussed in this talk (2507.14283) is the consistency between lattice and experimental results bridged through Effective Field Theories.

We find that, indeed, new finite-volume results reduce the systematic uncertainties in resonance parameter determination, when appropriately added to the experimental measurements. Predictions are made for the not yet established isovector states, showing larger systematic uncertainties.

Speaker: Maxim Mai (University of Bern)

MM-L1405.pdf

210 Negative parity hyperons from coupled channel scattering

The experimentally challenging J^P=1/2^- hyperons are investigated by computing meson-baryon scattering on the lattice. An ensemble with 2+1 flavours from the CLS consortium with m_pi=285 MeV, m_K=460 MeV is employed. This is possible thanks to the stochastic Laplacian Heaviside smearing. Both single hadron and scattering operators are considered in different irreps and moving frames. We will review the results for the Lambda(1405) channel, and the ongoing analyses of the Sigma(1430) and Xi(1620) will be discussed. For the latter we study meson-baryon scattering with three coupled channels.

Speaker: Fernando Alvarado (GSI)

211 Baryon masses with C-periodic boundary conditions

Isospin-breaking corrections pose a significant challenge to lattice simulations, both because of the splitting between the up and down quark masses and, in particular, the need to include QED effects. The RC$*$ collaboration has developed the openQxD code, based on openQCD, which enables fully dynamical QCD+QED simulations through the implementation of C-periodic boundary conditions.
We use this code to measure baryon masses, with a special focus on the Ω⁻ baryon mass, whose precise determination is especially important since it has been used to set the scale of lattice simulations.
Due to the use of C-periodic boundary conditions, the two-point function of the Ω⁻ baryon gets additional partially connected contributions, which vanish in the infinite-volume limit and which we are computing for the first time.
We will present preliminary results for baryon masses obtained on QCD ensembles with C-periodic boundary conditions, at an unphysical pion mass of approximately 400 MeV.

Speaker: Sara Rosso (Consejo superior de investigaciones cientificas (CSIC), Humboldt University)

212 Dbar-N interaction from Lattice QCD at the physical point

The Dbar-N two-body system is one of the most fundamental systems involving open-charmed mesons and nucleons. Owing to the absence of quark-antiquark annihilation, the Dbar-N channel is an entirely exotic channel, such that a bound state would correspond to a pentaquark state. While some EFT models predict a strong attraction that could form a pentaquark state, other models suggest only weak attraction or even repulsion, implying no such state [1-5]. Realistic lattice QCD simulations can thus play a crucial role in clarifying the existence (or absence) of a pentaquark state in the Dbar-N channel.
In this talk, we present results for the Dbar-N potential and its s-wave scattering parameters obtained using the HAL QCD method [6,7] . (2+1)-flavor lattice QCD simulations were performed at the physical point with gauge configurations generated by the HAL QCD Collaboration (“HAL-conf-2023” [8]) on a $96^3 \times 96$ lattice with a pion mass $m_\pi \simeq 137$ MeV and lattice spacing $a \simeq 0.0844$ fm. We observe an attractive phase shift in the low-energy region of the I=0 channel and a repulsive phase shift in the I=1 channel. Our results indicate the absence of pentaquark states in both I=0 and I=1 channels.

[1] J. Hoffman, M.F.M. Lutz, Nucl. Phys. A 763 (2005) 90-139
[2] J. Haidenbauer, G. Krein, U.-G. Meissner, A. Sibirtsev, Eur. Phys. J. A33 (2007) 107-117
[3] D. Gamermann, C. Garcia-Recio, J. Nieves, L.L. Salcedo, L. Tolos, Phys. Rev. D 81 (2010) 094016
[4] C. E. Fontoura, G. Krein, V. E. Vizcarra, Phys. Rev. C 87 (2013) 025206
[5] Y. Yamaguchi, S. Yasui, A. Hosaka, Phys. Rev. D 106 (2022) 094001
[6] N. Ishii, S. Aoki, and T. Hatsuda, Phys. Rev. Lett. 99 (2007) 022001
[7] N. Ishii et al. (HAL QCD collaboration), Phys. Lett. B 712 (2012) 437-441
[8] T. Aoyama et. al. (HAL QCD collaboration), Phys. Rev. D 110 (2024) 9 094502

Speaker: Rento Yamada (RIKEN)

Quark and lepton flavor physics

Convener: Francesco Sanfilippo (INFN Roma Tre)

213 Study on the systematic effects on $b\to c$ inclusive semileptonic decays

We discuss the calculation of the inclusive semileptonic decay for the process $B_s \to X_c \, l\nu_l$ using lattice QCD, which could be decisive in understanding the long-standing tension between inclusive and exclusive determinations of the CKM matrix element, $|V_{cb}|$. In this talk, we investigate the main sources of systematic uncertainty in these decays, including the impact of Jacobi smearing at the source and sink, variations in source–sink separation, and the intrinsic uncertainties of the inclusive reconstruction method itself. To investigate the latter, we restrict the reconstruction of the inclusive decay rate to just the excited-state contributions. We achieve this by treating the ground-state contributions as an exclusive decay with well-controlled conventional techniques. Systematic effects from the reconstruction then only affect excited-state contributions. Where these are sub-dominant, a suppression of systematic effects is expected. We show results based on Chebyshev reconstruction, which are part of a larger effort towards a first phenomenologically relevant computation of the inclusive decay rate in the continuum and infinite-volume limits.

Speaker: Ahmed Elgaziari (University of Southampton)

214 Real radiative decays of heavy pseudoscalar mesons

The unitarity of the CKM matrix is a fundamental property of the Standard Model, and leptonic decays of pseudoscalar mesons $P \to \ell\nu(\gamma)$ are an important avenue to probe this experimentally. The theoretical prediction of the decay rate depends on a number of form factors, which can be calculated using lattice QCD. We present an approach to compute them using a JLQCD domain-wall fermion ensemble with $m_\pi=284~\text{MeV}$ and $a=0.044~\text{fm}$. We focus on the radiative decay $P \to \ell\nu\gamma$, where the photon is on-shell and $P$ is either a $D$, a $D_s$ or a $B$. The determination of the corresponding vector and axial form factors $F_V$ and $F_A$ give access to $|V_{cd}|$, $|V_{cs}|$, and $|V_{ub}|$.

Speaker: Teseo San Jose (University of Edinburgh)

215 Inclusive semileptonic decays of heavy mesons from lattice QCD

A first-principles computation of the inclusive semi-leptonic decay rates of heavy mesons from lattice QCD has a great phenomenological relevance since the comparisons of the theoretical results with the corresponding experimental data allows for stringent Standard Model tests in the sector of Flavour physics. In this talk we present the first fully non-perturbative computation of the $D_s \to X\ell\nu$ decay rate and of the associated leptonic moments, carried out on state-of-the-art ETMC ensembles at the physical point with four lattice spacings and three volumes. The extraction of the relevant smeared spectral densities from Euclidean four-point correlation functions has been performed with controlled statistical and systematic uncertainties by using the Hansen-Lupo-Tantalo method. Additionally, we present preliminary results of our ongoing calculation of the inclusive semi-leptonic $B$ mesons decay rates with focus on some important technical aspects of the calculation.

Speaker: marco garofalo (University of Bonn, HISKP)

216 Ground-State Extraction of Heavy-Light-Meson Semileptonic Decay Form Factors

We discuss the extraction of form factors for heavy-light pseudo-scalar to light pseudo-scalar decay form factors from finite time correlation functions. Particular emphasis is placed on controlling the contamination from excited-states using also the information from chiral perturbation theory to isolate the ground-state contribution. The analysis is performed on CLS ensembles with $N_f = 2+1$ flavours of $\mbox{O}(a)$-improved Wilson fermions (presently) at the $\mathrm{SU}(3)$-symmetric point with relativistic heavy-quark masses in the charm region and above. Our form factors will be used in a computation of the $B \to \pi$ form factors combining the continuum-limit relativistic results with static-limit calculations.

Speaker: Antonino D'anna (INSTITUTO DE FISICA TEORICA, UAM-CSIC)

217 The smeared R-ratio in isoQCD from first-principles lattice simulations

The R-ratio is a phenomenological observable of great relevance, both in itself and in applications such as the dispersive approach to the muon anomalous magnetic moment. It can be investigated from first-principles in lattice QCD by introducing an arbitrary smearing kernel and employing the well-known Hansen-Lupo-Tantalo method to perform spectral reconstruction with controlled statistical and systematic errors. Improving upon a first study published in 2023, we show preliminary results using the correlation functions produced by ETMC in Nf = 2 + 1 + 1 lattice simulations at four lattice spacings, different volumes and with higher statistics w.r.t. our previous study. The new correlators, thanks to the implementation of the Low Mode Average technique, allow the determination of the R-ratio smeared with Gaussian kernels of widths down to σ ∼ 200 MeV with phenomenologically relevant precision.

Speaker: Francesca Margari (University of Rome Tor Vergata)

218 Study of the Λ → p ℓ ν ˉ semileptonic decay in lattice QCD

We present the first lattice QCD determination of the Λ→N vector and axial-vector form factors, which are essential inputs for studying the semileptonic decay Λ→pℓνˉ. This channel provides a clean, theoretically controlled avenue for extracting the CKM matrix element ∣Vus∣ from the baryon sector. Our analysis uses a gauge ensemble with physical light, strange, and charm quark masses and yields the most precise determination to date of the full set of transition form factors -- including second-class contributions -- as well as the associated couplings, radii, and the ratio of muon-to-electron decay rates, an observable sensitive to possible non-standard scalar and tensor interactions. We compare our non-perturbative results with next-to-next-to-leading order expansions in the small parameter δ=(mΛ−mN)/mΛ≈0.16. We find that the common phenomenological approximation of neglecting the q^2-dependence of the form factors leads to a ∼4% deviation in the decay rate. This underscores the critical importance of precise, fully non-perturbative form factor inputs for achieving the sub-percent precision targets of upcoming experimental programs. (See https://inspirehep.net/literature/2945864)

Speaker: Andreas Konstantinou (University of Cyprus)

Structure of hadrons and nuclei

Convener: Gunnar Bali (Universität Regensburg)

219 Nucleon isovector electromagnetic form factors from $N_f=2+1$ CLS ensembles

We present progress towards a high-precision lattice QCD study of the nucleon’s isovector vector form factors, which encode key aspects of the nucleon’s spatial structure and its response to electromagnetic probes. We utilize the Coordinated Lattice Simulations (CLS) ensembles generated with $N_f =2+1$ non-perturbatively $O(a)$ improved Wilson fermions and a tree-level Symanzik-improved gauge action. The over 50 ensembles available provide a wide coverage of the quark mass plane and comprise six lattice spacings, enabling control of both the quark mass and continuum extrapolations. We present a preliminary analysis on a subset of these ensembles. A major challenge in extracting the form factors is the treatment of excited-state contamination, which is addressed by executing multi-state fits stabilized with data-driven priors. The results for the form factors, over all ensembles, are simultaneously fitted, where we utilize the z-expansion to parameterize the dependence on the momentum transfer.

Speaker: Marcel Rodekamp (Universität Regensburg)

220 Flavor structure of the nucleon axial form factor from lattice QCD

We present our work on the computation of the axial form factor of the nucleon from lattice QCD. We employ a set of $N_f=2+1$ CLS ensembles with $O(a)$-improved Wilson fermions and the Lüscher-Weisz gauge action, with lattice spacings ranging from $0.05\,\text{fm}$ to $0.086\,\text{fm}$ and pion masses spanning between $130\,\text{MeV}$ and $350\,\text{MeV}$. To control excited-state effects, we employ multiple source–sink separations in combination with the summation method. The $Q^2$-dependence of the form factors is parametrized using the $z$-expansion, and we perform simultaneous fits of all available source–sink separations for $Q^2\leq 0.7 \,{\rm GeV}^2$. We summarize the results of the isovector and isoscalar octet form factors and report on ongoing work towards the isoscalar singlet channel and the full flavor decomposition, with particular focus on the strange-quark contribution.

Speaker: Alessandro Barone (Johannes Gutenberg University Mainz)

221 Pressure-Energy Equations of State of Hadrons

From the conservation of the energy-momentum tensor, we show that the pressure distribution in the hadrons are due to the difference of the trace and traceless parts of the spatial distribution of T^{ii}, which can be obtained from the gravitational form factor
A (q^2) and the mass form factor G_m (q^2). Furthermore, we derive the pressure-energy equations of state for the respective traceless and traceless parts. We use lattice results to illustrate this point. We also point out that they are the same as for the vortices of type-II superconductors and in the standard \Lambda CDM model in cosmology.

Speaker: Kehfei Liu

222 Nucleon strange electromagnetic form factors using $N_f=2+1+1$ twisted-mass fermions at the physical point

We present the strange electromagnetic form factors of the nucleon using lattice QCD with $N_f=2+1+1$ twisted mass clover-improved fermions and quark masses tuned to their physical values. Using four ensembles with lattice spacings of $a=0.080$ fm, $0.068$ fm, $0.057$ fm and $0.049$ fm, and similar physical volume, we obtain the continuum limit directly at the physical point. The disconnected strange contributions are computed using high statistics two-point functions combined with stochastic noise mitigation techniques such as spin-color dilution and hierarchical probing in the estimation of the quark loop. Studying the momentum dependence of the form factors, we provide the strange electric and magnetic radii, as well as the strange magnetic moment in the continuum limit.

Speaker: Bhavna Prasad (The Cyprus Institute)

Theoretical developments and applications beyond Standard Model

Convener: Biagio Lucini (Queen Mary University of London (UK))

223 Glue Condensate, Quark Condensate and Dirac Spectral Density

I derive the regularized formula for glue scalar density (gluon
condensate) in terms of Dirac spectral density [arXiv:2509.03509],
and elaborate on its uses and meaning. Particular attention will
be given to understanding of what this new formula reveals about
the relation between glue and quark scalar densities, how it
clarifies the distinction between anomalous and spontaneous ways
of breaking symmetries, and what it says about the relation
between UV and IR in QCD.

Speaker: Ivan Horvath

224 Topology and Banks-Casher relation using Minimally Doubled Fermions

We determine the role of topology from the eigenmodes, and extract the chiral condensate from the eigenvalue density of minimally doubled fermions (MDF), namely in Karsten-Wilczek (KW) and Borici-Creutz (BC) formulations. We employ MILC asqtad ensembles with $N_f=2+1$ dynamical flavors of quarks [1] as backgroud gauge fields. Using flavored mass terms [2,3], we find that the spectral flow of the eigenvalues correctly detects the topology of the background gauge field. The modified chiralities of the zero eigenmodes take the value $\approx0.9$. The non-zero eigenmodes have chiralities of $\mathcal{O}(10^{-2})$ and form clusters of doublets. The chiral condensate extracted via the eigenvalue density using the Banks-Casher relation is compared to the direct calculation of the chiral condensate obtained by inverting the Dirac matrix.

[1] C. W. Bernard, T. Burch, K. Orginos, D. Toussaint, T. A. DeGrand, C. E. Detar, S. Datta, S. A. Gottlieb, U. M. Heller, and R. Sugar, Phys. Rev. D 64, 054506 (2001), arXiv:hep-lat/0104002.
[2] M. Creutz, T. Kimura, and T. Misumi, JHEP 12, 041, arXiv:1011.0761 [hep-lat].
[3] S. Dürr and J. H. Weber, Phys. Rev. D 105, 114511 (2022), arXiv:2203.15699 [hep-lat].

Speaker: Abhijeet Kishore (Indian Institute of Technology Kanpur)

225 Finite-temperature Sp(4) Yang-Mills theory: towards the continuum

We present new results for Sp(4) Yang-Mills theory around its first-order thermal phase transition by reconstructing the density of states via the LLR algorithm. We show results on different space and time extents, as well as aspect ratios, and estimate discretization artifacts. We see clear signatures of the first-order transition and determine the critical coupling, the specific heat and set bounds on the surface tension.

Speaker: Fabian Zierler (Swansea University)

226 Moment problems and spectral functions

Methods based on analyticity, such as Nevanlinna-Pick interpolation, have the promise of providing rigorous constraints on real-time observables (e.g. spectral functions), assuming only causal consistency of the underlying euclidean data. In this talk, I will review recently discovered connections between Nevanlinna-Pick interpolation and moment problems, which provide a discrete euclidean time analog to Nevanlinna-Pick interpolation for reconstructing spectral functions, as well connections to Krylov-space methods for correlator analyses (Lanczos/Rayleigh-Ritz).

Speaker: Ryan Abbott (Columbia University)

227 Non-perturbative renormalization of the energy momentum tensor in the 2d O(3) nonlinear sigma model

The two-dimensional O(3) nonlinear sigma model is a well known toy model for studying non-perturbative phenomena in quantum field theory and QCD in particular. A central challenge is the renormalization of the energy-momentum tensor, which is complicated by nonlinear Ward identities constraining operator mixing and by large cutoff effects affecting the determination of renormalization constants. To address these issues, we employ a modified lattice action with shifted boundary conditions and define the coupling through the gradient flow at vanishing topological charge. Within this framework, we present preliminary results for the non-singlet sector, demonstrating the feasibility of our approach. These results provide a basis for comparing different strategies to determine renormalization constants, a direction we plan to pursue in future work.

Speaker: Mika Lauk (HU-Berlin)

228 Critical Phenomena on Bethe Lattice

We investigate the critical behaviour of a $\mathbb{Z}_2$-symmetric scalar field theory defined on Bethe lattices (the tree limit of regular hyperbolic tessellations) using both lattice perturbation theory and the non-perturbative functional renormalization group. Owing to the hyperbolic nature of such graphs, the Laplacian lacks a zero mode and exhibits a spectral gap, which is an external scale in the system, hindering the computation of critical exponents. Closing the spectral gap by adding a negative mass to the bare Laplacian is therefore essential to access a nontrivial fixed point, whose critical exponents are governed by the spectral dimension, which is three, corresponding to the Wilson–Fisher universality class. This behavior stands in stark contrast to the nearest‐neighbor Ising model on Bethe lattices, which has mean‐field critical exponents. To our knowledge, this constitutes the first explicit demonstration that a $\phi^4$ theory and the discrete Ising model may flow to distinct fixed points on the same underlying lattice. We further comment on possible reasons for such deviations and propose future work to better understand critical phenomena on more general hyperbolic spaces.

Speaker: Saswato Sen (Okinawa Institute of Science and Technology)

16:30 Coffee break

Cultural Event

Banquet

Friday 7 November

Plenary session

Convener: Leonardo Giusti (University of Milano-Bicocca and INFN)

229 Lattice Gauge Theory Contributions to Quark Flavour Physics

Many observables used to extract Standard Model parameters and to
constrain New Physics in the quark-flavour sector rely on lattice inputs.
I will review the current status and recent developments in these
determinations, with emphasis on controlling dominant sources of
systematic uncertainties.

Speaker: Gregorio Herdoiza

230 Hadron Structure in the Context of the EIC Program

I will review recent progress in our understanding of hadron structure, with emphasis on lattice-QCD calculations that directly support the scientific goals of the upcoming Electron-Ion Collider (EIC). I will discuss results for pion, kaon, and proton form factors, the computation of Mellin moments, and recent advances in the direct calculation of generalized parton distributions (GPDs). These developments highlight the growing interplay between lattice gauge theory and the experimental program at the EIC.

Speaker: Constantia Alexandrou (University of Cyprus & The Cyprus Institute)

11:00 Coffee break

Plenary session

Convener: Constantia Alexandrou

231 Lattice Calculations of Neutron Electric Dipole Moment

Recent lattice QCD calculations of the neutron and proton electric dipole moments (EDMs) and the CP-violating $\pi {\rm NN}$ coupling constant due to the $\theta$ term are reviewed. Progress towards nucleon EDM calculations, including the Weinberg three-gluon operator, and the quark chromoelectric dipole moment operator and their renormalization, is also discussed.

Speaker: Kehfei Liu

232 Current-Enhanced Excited States in Lattice QCD Three-Point Functions

Excited-state contamination remains one of the leading sources of systematic uncertainty in the precise determination of hadron structure observables from lattice QCD. In this talk, I will discuss a general argument, inspired by meson dominance and implemented through the variational method, to identify which excited states are enhanced by the choice of the inserted current and kinematics. The argument is supported by numerical evidence across multiple hadronic channels, in particular in the nucleon sector, and provides both a conceptual understanding and practical guidance to account for excited-state effects in hadron three-point function analyses.

Speaker: Lorenzo Barca (DESY)

233 Wilson Award

13:15 Lunch break

Algorithms and artificial intelligence

Convener: Roman Gruber

234 Diffusion Models for Sampling on SU(N)

Ensemble generation remains a central challenge in lattice field theory simulations, as traditional MCMC algorithms suffer from long autocorrelation times. Recent advances in generative modeling, including diffusion models, offer accelerated approaches for sampling complicated probability distributions. In this work, we present a diffusion-based framework for sampling ${\rm SU}(N)$ degrees of freedom. We adapt the traditional score matching technique for training diffusion models to the ${\rm SU}(N)$ group manifold and demonstrate that our models faithfully reproduce both the heat kernel evolution as well as a family of target densities for toy theories. By solving the reverse-time ODE directly on the group, we can efficiently generate unbiased ${\rm SU}(2)$ estimates from single-site toy models. These results mark a step for diffusion models towards modeling full ${\rm SU}(N)$ lattice field theories and, ultimately, ${\rm SU}(N)$ gauge theory on the lattice.

Speaker: Octavio Vega (University of Illinois Urbana-Champaign)

235 Machine Learning Kernels for Real-Time Complex Langevin

Real time evolution in QFT poses a severe sign problem, which may be alleviated via a complex Langevin approach.
However, so far simulation results consistently fail to converge with a large real-time extent. A kernel in a complex Langevin equation is known to influence the appearance of the boundary terms and integration cycles, and thus kernel choice can improve the range of real-time extents with correct results. For multi-dimensional models the optimal kernel is searched for using machine learning methods. We test this approach by simulating the simplest possible case, a 0+1-dimensional scalar field theory in Minkowski space

Speaker: Enno Carstensen (University of Graz)

236 Sampling from a complex distribution using an Energy-based Diffusion model

Complex langevin for theories with a sign problem effectively sample from a real-valued probability distribution that is a priori unknown and notoriously hard to predict. In generative AI, diffusion models can learn distributions from data. In this contribution, we investigate their ability to capture the distributions sampled by a complex Langevin process, comparing score-based and energy-based approaches, and outlining potential applications.

Speaker: Diaa Eddin Habibi (Swansea University)

237 Generative sampling with physics-informed kernels

Approaching the continuum limit in a lattice field theory is an important but computationally difficult problem. Here, on the one side, most traditional Monte Carlo methods suffer from critical slowing down. On the other side, generative models find it increasingly difficult to learn the map from a simpler to the targeted theory.

To tackle this problem, we construct a generative model using the physics-informed renormalisation group. Here, the layered map is trained and optimised independently on each layer. For each layer, the training boils down to solving an independent linear differential equation. This potentially parallelises the training procedure. Moreover, because the differential equation is analytically given, it allows for a systematic error correction and improvement beyond training time. This is done without requiring samples from the targeted theory. These features pave the way for future research and enable a systematic correction and design of generative models for lattice field theories. We illustrate the practical feasibility of the architecture within simulations of scalar field theories.

Speaker: Renzo Kapust (Institute for theoretical Physics, University of Heidelberg)

Hadronic and nuclear spectrum and interactions

Convener: Amy Nicholson (UNC Chapel Hill)

238 Physical-point lattice QCD study of baryon-baryon interactions in the $S = -1$ channel

We present first-principles lattice QCD results for the strangeness $S = -1$ sector of baryon-baryon interactions with the physical masses for the first time. Employing the (2+1)-flavor gauge configurations (HAL-conf-2023) [1] generated on the physical point, $(m_\pi , m_K) = (137, 502)~\mathrm{MeV}$, we calculate baryon-baryon correlation functions using the supercomputer Fugaku and extract potentials by the HAL QCD method [2]. We analyze the coupled-channel potentials for $N\Lambda$-$N\Sigma$ ($I = 1/2, ^1S_0$ and $^3S_1$) and the potentials for $N\Sigma$ ($I = 3/2$, $^1S_0$ and $^3S_1$). We compare our results with the data, including phase shifts in scattering experiments and femtoscopic correlation functions in high-energy collisions for $\Sigma^+ p$ [3,4].

Speaker: Koichi Murase (Osaka University)

239 Preliminary study of the $H$ dibaryon in $N_f=2+1$ lattice QCD

We present preliminary results on the $I=0$, $S=-2$ $H$ dibaryon in $N_f=2+1$ QCD. The calculation is performed with heavier-than-physical quarks ($m_\pi \approx 280$ MeV) on a single CLS ensemble. Correlation matrices are constructed using the distillation technique and the three relevant channels, $\Lambda\Lambda$, $N\Xi$, $\Sigma\Sigma$, are investigated to determine the interacting spectrum relevant for S-wave across multiple momentum frames. The scattering amplitude is investigated by solving the corresponding two-body quantization condition. These preliminary results are part of the ongoing efforts to determine the properties of hyperons and to establish whether a bound $H$ dibaryon exists down to physical quark masses.

Speaker: Davide Laudicina (Ruhr Universität Bochum)

240 Systematic uncertainties in lattice QCD calculations of multi-hadron systems

Excited-state effects lead to hard-to-quantify systematic uncertainties in spectroscopy calculations when imaginary times are smaller than inverse excitation gaps. The recently proposed Lanczos/Rayleigh-Ritz framework provides a set of two-sided constraints on energy levels that hold regardless of the size of excited-state effects. In this talk I discuss the application of these newly developed techniques to a high-statistics two-nucleon dataset computed at quark masses corresponding to a pion mass of 800 MeV.

Speaker: Robert Perry (Massachusetts Institute of Technology)

241 Investigating Quark Mass Dependence of Nuclear Binding

We present preliminary results from a lattice QCD study of the lowest energy levels of light nuclei—specifically the deuteron, dineutron, helium-3, and helium-4 systems—and compare those with their respective thresholds for investigating their binding energies. We utilize a set of $N_f=2+1$ flavor gauge ensembles, generated by the HotQCD Collaboration with the HISQ action at the physical sea quark masses and at lattice spacing $a = 0.076$ fm, while the valence sector employs clover fermions.
Calculations are performed at three valence pion masses $m_{\pi}\approx140$ MeV, $300$ MeV and $700$ MeV, employing both asymmetric and symmetric source-sink setup using a large statistics, with a goal to
explore the quark-mass dependence of nuclear bindings. The resulting correlation functions are analyzed using the standard vanila fitting, ratio correlators, as well as by employing the recently proposed transfer-matrix generalized eigenvalue problem (TGEVP) formalism.

Speaker: Debsubhra Chakraborty (Tata Institute of Fundamental Research (TIFR), Mumbai)

242 Quark mass dependence of the nuclear LS force

We study the nucleon-nucleon interactions in the parity-odd sector with lattice QCD. The central, tensor, LS forces are determined by the HAL QCD method. Gauge configurations with three different quark masses, corresponding to $m_\pi=840, 670, 470\,\rm{MeV}$, are employed to examine the quark mass dependence. All-to-all propagators are computed with a free Laplacian Heaviside (fLapH) method, which utilizes the low-mode dominance with drastically reduced computational cost compared to that of the conventional covariant Laplacian Heaviside (cLapH or LapH in the literature) method.

Speaker: Takuya Sugiura

QCD at nonzero temperature and density

243 Phase structure of lattice QCD in the heavy quark high-density region and the three-state Potts model

The nature of the finite temperature phase transition of QCD depends on the particle density and the mass of the dynamical quarks. It is known that the transition is first order in the region of zero density and heavy quark mass, and also first order in the region of light quark mass when the number of flavors is large. The intermediate region is the crossover region, and numerical simulations of lattice QCD have shown that the critical mass at which the first-order phase transition turns into a crossover in the heavy quark region increases with increasing density. When investigating high-density regions in lattice QCD simulations, a problem known as the sign problem arises, making research difficult. However, in regions where quarks are sufficiently heavy, the sign problem is relatively less serious, making research possible. On the other hand, the critical mass at which the first-order phase transition in the light quark region ends is also expected to increase with increasing density. If the region of the first-order phase transition in the light quark regime continues to expand with increasing density, the critical point should reach the heavy quark region where it can be studied.
In this study, we discuss whether there is a first-order phase transition region in the heavy quark high-density region that is different from the first-order phase transition in the low-density region. There is an effective theory that describes the heavy quark high-density limit of QCD. This effective theory is a simple model in which the Polyakov loop is a dynamical variable, and the quark Boltzmann factor is controlled by only one parameter, $C(\mu,m)$, which is a function of the mass $m$ and the chemical potential $\mu$. The Polyakov loop is the order parameter of the Z(3) symmetry that is broken at the finite-temperature phase transition of QCD. We consider that the fundamental properties of a phase transition are determined only by the symmetry broken by the phase transition and the dimension of the space. By using an approximation in which the Polyakov loop is replaced by a Z(3) spin, we find that the effective model is a three-dimensional three-state Potts model (Z(3) spin model) with a complex external field term. We investigate the phase structure of the Potts model and apply it to QCD in the heavy quark region. As the density varies from $\mu=0$ to $\mu=\infty$, we find that the phase transition is first order in the low-density region, changes to a crossover at the critical point, and then becomes first order again. This strongly suggests the existence of a first order phase transition in the high-density heavy quark region of QCD.

Speaker: Shinji Ejiri (Niigata University)

244 QCD in strong magnetic fields: fluctuations of conserved charges and EoS

Strong magnetic fields can profoundly affect the equilibrium properties, characterized by the equation of state and bulk thermodynamics of strongly interacting matter. Although such fields are expected in off-central heavy-ion collisions, directly measuring their experimental imprints remains extremely challenging. To address this, in this talk we propose the baryon-electric charge correlations $\chi^{\rm BQ}_{11}$ and the chemical potential ratio $\mu_{\rm Q}/\mu_{\rm B}$ as magnetic-field-sensitive probes, based on (2+1)-flavor QCD lattice simulations at physical pion masses. Along the transition line, $\chi^{\rm BQ}_{11}$ and $(\mu_{\rm Q}/\mu_{\rm B})_{\rm LO}$ in Pb--Pb collisions increase by factors of 2.1 and 2.4 at $eB \simeq 8M_\pi^2$, respectively. To bridge theoretical predictions and experimental observations, we construct HRG-based proxies and apply systematic kinematic cuts to emulate STAR and ALICE detector acceptances. Furthermore, extending this investigation, we discuss the QCD equation of state and examine the leading-order thermodynamic coefficients for strangeness-neutral scenarios up to $eB \simeq 0.8 {\rm GeV}^2 \sim 45 m_{\pi}^2$, revealing intriguing non-monotonic structures.

Speaker: Arpith Kumar (Central China Normal University)

245 Deconfinement and chiral aspects of the QCD crossover under magnetic fields: static-quark entropy and chiral susceptibility

We investigate the static-quark entropy in QCD in the presence of external magnetic fields, using its temperature peak as a pseudocritical deconfinement indicator. Our calculations employ HISQ fermions with a tree-level improved Symanzik gauge action at physical quark masses, on lattices with temporal extents $N_\tau = 8, 12$ and fixed aspect ratio $N_\sigma/N_\tau = 4$. A two-dimensional $(T, eB)$ analysis allows us to determine $S_Q(T, eB)$, from which we extract $T_{pc}^{Q}(eB)$ and perform a continuum extrapolation.  

In the weak-field region studied, $T_{pc}^{Q}(eB)$ exhibits a mild decrease, from $\sim 155$~MeV at $eB=0$ to $\sim 152$~MeV at $eB = 0.14\,\mathrm{GeV}^2$. We compare this deconfinement indicator with the total chiral susceptibility and the baryon-electric charge correlation $\chi^{BQ}_{11}$ to explore their distinct responses in the $T-eB$ plane.

Speaker: rishabh thakkar (Central China Normal University)

246 QCD Anderson transition with overlap valence quarks and influence of external magnetic fields

The QCD Anderson transition is believed to be connected to both, confinement and chiral symmetry breaking. We investigate the latter relation by studying the low-lying eigenmodes of the overlap operator in the background of gauge configurations with 2+1+1 quark flavors of twisted-mass Wilson fermions. The mobility edge, below which eigenmodes are localized, is estimated by the inflection point of the relative volume. Contrary to the previous prediction 1, this estimate does not vanish at the temperature of the chiral phase transition 2. We discuss a possible scenario, supported by literature, for why this could be the case and present an alternative observable as a measure of localization.
Since it is known that external magnetic fields reduce the chiral as well as the deconfinement transition temperature, the second part proceeds with a study of staggered fermions in the presence of different magnetic field strengths. First results will be presented and the apparent influence on the QCD Anderson transition will be discussed.

[1] R. Kehr, D. Smith, L. von Smekal, PRD 109 (2024) 074512.
[2] R. Kehr, L. von Smekal, PoS LATTICE2024 (2025) 189.

Speaker: Robin Kehr (Justus Liebig University Giessen)

247 Inhomogeneous condensate and phase structure in the (1+1)d Gross–Neveu Model based on an Extended k-Shape Method

We present an extended version of the k-Shape method, originally developed for time-series clustering, and apply it to lattice simulations of the finite-temperature and finite-density (1+1)-dimensional Gross–Neveu model. The method has been generalized from real to complex scalar fields and from one-dimensional to multidimensional configurations, allowing a detailed analysis of spatially varying condensates.
By employing the extended k-Shape method, we can extract detailed information about phase structure that is not easily accessible through conventional techniques. In the uniform, chiral-symmetry-broken phase, the phase structure can be characterized sufficiently by the expectation value of the configuration. Near the phase boundary, however, the k-Shape method reveals smooth variations in the configuration pattern, providing a sensitive probe of the transition region.The extended k-Shape method can analyze spatial dependencies that do not resemble simple sinusoidal waves. This makes it particularly suitable for identifying nontrivial spatial patterns that emerge in inhomogeneous condensate. In kink-like configurations, for example, the minimum of the correlation function is not necessarily negative, indicating a richer structure than can be captured by traditional correlation analysis.
These results demonstrate that the k-Shape approach offers a powerful and versatile framework for extracting detailed features of phase transitions and for exploring the interplay between uniform and inhomogeneous condensate in lattice field theories.

Speaker: Chiho Nonaka (Hiroshima University)

Quantum computing and quantum information

Convener: Bipasha Chakraborty (University of Southampton)

248 Ground state energy of the two-dimensional pure $\mathbb{Z}_2$ lattice gauge theory via quantum imaginary time evolution.

The quantum imaginary time evolution (QITE) is a quantum algorithm that approximates imaginary-time evolution using unitary operators.
We apply the QITE to the two-dimensional pure $\mathbb{Z}_2$ lattice gauge theory to obtain the ground state energy. In addition, we estimate the algorithmic and statistical errors and computational costs via classical simulation. It was also shown in the previous work in the context of spin models that one can construct the unitary operators while preserving (global) symmetry, which reduces the gate count. We utilize the same method for the local gauge constraints (Gauss’s law) and demonstrate a reduction in gate cost.

Speaker: Minoru SEKIYAMA (UTokyo School of Science)

249 Ground state energy of a two-dimensional pure Z2 lattice gauge theory via sample-based quantum Krylov diagonalization

We study the ground state energy of a two-dimensional pure $\mathbb{Z}_2$ lattice gauge theory (LGT) on a triangular lattice by applying the sample-based quantum Krylov diagonalization. Moreover, an error detection and mitigation method based on Gauss’s law constraints is incorporated. We demonstrate this method in the $\mathbb{Z}_2$ LGT using the IBM quantum hardware and classical tensor network simulation, and investigate the errors arising from the algorithm and hardware noise.

Speaker: Dr Lento Nagano (University of Tokyo (JP))

250 A Study of Entanglement and Ansatz Expressivity for the Transverse-Field Ising Model using VQE

The Variational Quantum Eigensolver (VQE) is a leading hybrid quantum-classical algorithm for simulating many-body systems in the NISQ era. However, its effectiveness relies not only on accessing ground-state energies but also on preparing accurate eigenvectors, and the later is particularly challenging in degenerate and strongly entangled regimes. We investigate this problem using the transverse-field Ising model (TFIM) with periodic boundary conditions in one, two, and three dimensions, employing up to 27 qubits. We adopt two ansatzes - the physics-inspired Hamiltonian Variational Ansatz (HVA) and the hardware-efficient EfficientSU2 from Qiskit. We benchmark them using energy variance, entanglement entropy, spin correlations, and magnetization. We find that while entanglement entropy is well reproduced in 1D, higher-dimensional systems demand deeper circuits and longer optimization. EfficientSU2 provides smoother optimization and performs well in low-entanglement regimes but underestimates critical correlations. In contrast, HVA circuits capture the entangled ground-state structure near criticality, though with more rugged optimization landscapes. We further show that VQE offers complementary insights into entanglement scaling in 3D TFIM by directly accessing the reduced density matrix and von Neumann entropy—an advantage over Quantum Monte Carlo methods, which are limited to Rényi entropy. These results demonstrate practical benchmarks for ansatz-design as well as highlight entanglement and correlation measures as diagnostics for reliable variational simulations of lattice models.

Speaker: Ashutosh Tripathi (Tata Institute of Fundamental Research (TIFR), Mumbai)

251 Implementation and Optimization of the HHL Quantum Linear Solver

The Harrow–Hassidim–Lloyd (HHL) algorithm offers an exponential quantum speedup for solving sparse, well-conditioned linear systems of equations. We have implemented the HHL algorithm and evaluated its performance across systems of varying sparsity and recorded each class separately with sizes upto $N=1024$.

The principal bottleneck of HHL lies in Quantum Phase Estimation. To address this, we explored several approximation strategies: Suzuki–Trotter decomposition, a truncated Taylor series expansion, block encoding with quantum signal processing, and adiabatic-inspired evolution. These modifications substantially reduce circuit complexity and improve fidelity compared to naive implementations. In particular, Taylor expansion and block encoding consistently outperformed Trotterisation for less sparse systems, while Trotterisation was found to be suited to sparse systems.

Performance was measured using fidelity and execution time. Results on quantum simulators demonstrated high-fidelity solutions for sparse systems, while with dense systems the growing circuit depth lowers fidelity. These implementations were further tested on IBM Quantum hardware, which confirmed feasibility but revealed substantial noise and runtime overheads. Our results highlight the importance of matrix structure and Hamiltonian simulation strategy in practical HHL implementations, offering guidance for scaling the algorithm on near-term quantum devices.

Speaker: Dhruv Sood (Tata Institute of Fundamental Research)

252 Computing quantum entanglement with machine learning

Entanglement calculations in quantum field theories are extremely challenging and typically rely on the replica trick, where the problem is rephrased in a study of defects. We demonstrate that the use of deep generative models drastically outperforms standard Monte Carlo algorithms. Remarkably, such a machine-learning method enables high-precision estimates of Rényi entropies in three dimensions for very large lattices. Moreover, we propose a new paradigm for studying lattice defects with flow-based sampling.

Speaker: Andrea Bulgarelli (University of Turin and INFN Turin)

Quark and lepton flavor physics

Convener: Teseo San Jose (University of Edinburgh)

253 Exclusive $B\to\pi\ell\nu$ semileptonic decays with highly improved staggered quarks

We present new results on semileptonic decays of B-mesons using the highly improved staggered quark (HISQ) action for both valence and 2+1+1 sea quarks. Our calculation uses lattice spacings ranging from 0.12 fm down to 0.03 fm, including several ensembles with physical-mass pions. The focus on the talk will be on the vector and scalar form factors for the decay $B\to\pi\ell\nu$.

Speaker: William Jay (Colorado State University)

254 $B_{(s)} \to D_{(s)} \ell \nu$ form factors from $2+1+1$ flavor Lattice QCD

We present a calculation of the form factors for $B_{(s)} \to D_{(s)} \ell \nu$ decay using the highly improved staggered quark action for both valence and sea quarks on the MILC collaboration’s $2+1+1$-flavor ensembles with lattice spacings ranging from 0.09fm to 0.03fm, many with physical pion masses. On our finest ensembles, we can compute the form factors directly at the physical $b$-quark mass. In this talk, we present preliminary results of chiral-continuum fits for the scalar and vector form factors. The goal of this project is a percent level determination of the scalar and vector form factors to enable a high-precision determinations of $|V_{cb}|$. It fits into a broader program of lattice-QCD studies of weak $B$-meson decays by the Fermilab Lattice and MILC collaborations.

Speaker: Akhil Chauhan (University of Illinois Urbana Champaign)

255 Extracting $B_s\to D_s^*\ell\nu_\ell$ form factors

Semileptonic $B_{(s)}$ decays are of great phenomenological interest because they allow to determine e.g. CKM matrix elements or test lepton flavour universality.
Taking advantage of already existing lattice data, we demonstrate the analysis steps to extract the four form factors describing exclusive semileptonic
$B_s\to D_s^*\ell\nu_\ell$
decays using the narrow width approximation. Our data are based on RBC/UKQCD's set of 2+1 flavour gauge field ensembles with Shamir domain-wall fermion and Iwasaki gauge field action featuring inverse lattice spacings of $a^{-1}=$1.785, 2.383, and 2.785 GeV as well as pion masses between 268 and 433 MeV. Light, strange and charm quarks are simulated using domain-wall fermions, whereas bottom quarks are generated with the relativistic heavy quark (RHQ) action.

Speaker: Anastasia Boushmelev (University of Siegen)

256 Heavy Meson Lifetimes from Gradient Flow

Theoretical predictions for heavy meson lifetimes require high-precision determinations of the matrix elements involving four-quark operators using non-perturbative methods.
While similar operators relevant for neutral meson mixing have become standard for lattice QCD calculations, these lifetime operators suffer from complications in renormalisation where the dimension-six operators of interest mix with operators of lower mass dimension.

Fermionic gradient flow provides a renormalisation procedure where hadronic matrix elements on the lattice are evolved along the flow time and UV divergences are gradually removed.
The final result is obtained by matching to the $\overline{\rm MS}$ scheme using the short-flow-time expansion.
This method can circumvent challenges on the lattice such as mixing with operators of lower mass dimension.

Exploiting renormalisation group equations to further quantify the scale dependence, we present results for the four-quark operators contributing to the $D_s$ meson lifetime as well as prospects towards using this methodology for $B$ mesons.

Speaker: Matthew Black (University of Edinburgh)

257 Untangling the heavy-flavor mess: status of the Fermilab-MILC calculation of the $B_{(s)}\to D^{(\ast)}_{(s)}\ell\nu$ form factors

In this talk I will review the status of a calculation of the form factors of the most relevant heavy-to-heavy decay channels. Using seven N_f=2+1+1 HISQ ensembles, with lattice spacings ranging from 0.15 fm down to 0.06 fm, we calculate the form factors of the $B_{(s)}\to D_{(s)}^{(\ast)}\ell\nu$ decays, including correlations among them. More than half of our ensembles feature physical pion masses, and the heavy quarks $(b,c)$ are simulated at their physical masses using the Wilson-Clover action with the Fermilab interpretation.

Even though we have recently seen huge qualitative and quantitative leaps in the characterization of heavy-to-heavy decays, these advances have failed to translate into improvements for the $|V_{cb}|$ inclusive vs exclusive question, or the matter of the LFU ratios. In particular, in the $B\to D^{(\ast)}\ell\nu$ channel, the current situation of the lattice form factors is far from clear. The work presented here is an attempt to address these issues.

Speaker: Alejandro Vaquero Avilés-Casco (University of Zaragoza)

Theoretical developments and applications beyond Standard Model

Convener: Marcello Dalmonte (ICTP)

258 Generalizing the SU(3) loop-string-hadron formalism to multidimensional space

The loop-string-hadron (LSH) formulation for lattice gauge theories has been developed in the Hamiltonian framework for application in quantum simulation and tensor-network calculations. A major driver of its development has been eventual application to QCD. The LSH formalism for SU(2) gauge fields was quickly developed for coupling to staggered quarks, in 1D space, and in multidimensional space. Generalizing the formalism to SU(3) was straightforward for 1D space, but the generalization to multidimensional space has proven to be the most technically involved step. I will report on the status of this generalization, especially our recent usage of a basis that is nonorthogonal.

Speaker: Jesse Stryker (Lawrence Berkeley National Laboratory)

259 Interplay of Gauss Law and the fermion sign problem in quantum link models with dynamical matter

Quantum Link Models with dynamical matter coupled to spin-1/2 U(1) gauge fields in d=2+1 and 3+1 can give rise to phases expected in QED and beyond. Using exact diagonalization techniques, we show that the ground state is always the sector which satisfies (G_e,G_o) = (d,-d), where d is the spatial dimension and e and o are even and odd sites. It can be analytically proven that this sector is free of the fermion sign problem. We also demonstrate that a meron cluster algorithm for the problem naturally samples the ground states of the Hamiltonian in the aforementioned Gauss Law sector.

Speaker: PALLABI DEY (SAHA INSTITUTE OF NUCLEAR PHYSICS)

260 Confined and Deconfined Phases of Qubit Regularized Gauge Theories

We construct quantum Monte Carlo methods for simple qubit regularized gauge theories in various dimensions that do not suffer from sign problems. Results from these calculations suggest that these theories contain both confined and deconfined phases. Finite temperature phase transitions between these phases show the expected universality classes of traditional gauge theories in various dimensions. While quantum phase transitions are more difficult, we provide evidence for their feasibility.

Speaker: Prof. Shailesh Chandrasekharan (Duke University)

261 A novel Hamiltonian formulation of $1+1$ dimensional $\phi^4$ theory in Daubechies Wavelet Basis

We employ the wavelet formalism of quantum field theory to study field theories in the nonperturbative Hamiltonian framework. Specifically, we make use of Daubechies wavelets in momentum space. These basis elements are characterised by a resolution and a translation index that provides for a natural nonperturbative infrared and ultraviolet truncation of the quantum field theory. As an application, we consider the $1+1$ dimensional $\phi^4$ theory and demonstrate the emergence of the well-known nonperturbative strong-coupling phase transition in the $m^2 > 0$ sector. The critical coupling obtained through this approach is then compared with results from other methods previously reported in the literature.

Speaker: Mrinmoy Basak (Visiting Fellow, TIFR)

262 Lattice Field Theory for a Network of Real Neurons

In a recent paper [1], we introduced a simplified Lattice Field Theory framework that allows experimental observations from major Brain-Computer Interfaces (BCI) to be interpreted in a simple and physically grounded way. From a neuroscience point of view, our method modifies the Maximum Entropy Model for Neural Networks so that also the time evolution of the system is taken into account, and it can be interpreted as another version of the Free Energy principle. The framework is naturally tailored to interpret data from chronic multi-site BCI, especially spike rasters from measurements of single neurons activity.

[1] Neural Activity in Quarks Language: Lattice Field Theory for a Network of Real Neurons. Bardella, G.; Franchini, S.; Pan, L.; Balzan, R.; Ramawat, S.; Brunamonti, E.; Pani, P.; Ferraina, S., Entropy 26(6), 495 (2024). https://doi.org/10.3390/e26060495

Speaker: Simone Franchini (Sapienza Università di Roma)

Lattice Field Theory for a network of real neurons.pdf

16:10 Coffee break

Hadronic and nuclear spectrum and interactions

Convener: Robert Perry (Massachusetts Institute of Technology)

263 QCD Predictions for Physical Multimeson Scattering Amplitudes

We use lattice QCD calculations of the finite-volume spectra of systems of two and three mesons to determine, for the first time, three-particle scattering amplitudes with physical quark masses. Our results are for combinations of $\pi^+$ and $K^+$, at a lattice spacing $a = 0.063 ,\text{fm}$, and in the isospin-symmetric limit. We also obtain accurate results for maximal-isospin two-meson amplitudes, with those for $\pi^+K^+$ and $2K^+$ being the first determinations at the physical point. Results are compared to chiral perturbation theory and to phenomenological fits to experimental data.

Speaker: Fernando Romero López (Uni Bern)

264 Three-body study of the $T_{cc}^+$ from lattice QCD

In this talk, I discuss an ongoing first lattice study of the doubly-charmed tetraquark $T_{cc}^+(3875)$ via a fully three-body approach. We investigate the $DD\pi$ system in the $I = 0$, $C = 2$ sector, where the $T_{cc}^+$ appears as a pole in the $J^P = 1^+$ $DD\pi$ elastic scattering amplitude. The approach automatically incorporates two-body $DD^*$ and three-body $DD\pi$ effects and treats left-hand cuts due to single $\pi$ exchanges. Two CLS ensembles, X252 and X253, with pion mass $m_\pi \approx$ 280 MeV, are used and an operator set comprised of two-hadron, three-hadron and tetraquark operators is employed to extract finite-volume energies. Additional inputs are required for the three-body finite-volume analysis, in the form of amplitudes for the $I=1$ $DD$ and $I=1/2$ $D\pi$ two-body subsystems. I present preliminary results for these subchannels and perform exploratory three-body spectra determinations for simple choices of the three-particle K-matrix $\mathcal{K}_{3,\rm df}$, allowing a first comparison to the lattice spectrum.

Speaker: Andre Baiao Raposo (Ruhr-Universität Bochum)

265 Extending the finite volume formalism to the $N\pi\pi$ system at maximal isospin

We describe the extension of the relativistic field theoretic finite-volume formalism to $N \pi \pi$ scattering states at maximal isospin, $I=5/2$, focusing on the new features that arise in this system.
We illustrate the application of the formalism by providing a sample numerical application that includes the $\Delta$ resonance in the $N\pi$ subchannel.
We study the singularities in $N\pi\pi$ amplitudes arising from $N\pi\pi\pi$ intermediate states, and find that our subthreshold cutoff functions must be modified to avoid such singularities.
This is a step on the way to a formalism for the $I=1/2$ (Roper) channel,
which will require the inclusion of mixing with $N\pi$ states.
We explain why these cannot be included by treating the nucleon as a pole in $p$-wave $N\pi$ scattering, an approach that has been successful in studying $D D^*$ scattering using the three-particle $DD\pi$ formalism.

Speaker: Stephen Sharpe (University of Washington)

266 Emergence of the pi(1300) Resonance from Lattice QCD

What is the pattern and mechanisms behind the labyrinthine spectrum of excited hadrons?

Many open questions in this regard hinge on a precise understanding of the three-body dynamics in continuum and in finite-volume settings. One curious case is that of the lightest hadron — the pion — with the mass of 1/7th of that of the nucleon. Its excited state (pi(1300)) is nearly as heavy as the excited state of the nucleon (the Roper N*(1440)) — or 10 times as heavy as the ground state.

In my talk, I show how this problem can be tackled from Lattice QCD [https://arxiv.org/abs/2510.09476] from determining the finite-volume spectrum to mapping it to the infinite-volume amplitude and determining the resonance pole positions. Using partial input from CHPT, robust extrapolations to the physical point are made. Our results support the existence of the state (debated in some experimental analyses) overlapping with the average values from phenomenology.

Speaker: Maxim Mai (University of Bern)

MM-Pi1300.pdf

267 The structure of the lightest positive-parity charmed mesons from LQCD

The nature of low-lying scalar and axial-vector charmed mesons has long been debated, specifically whether they are best explained by hadronic molecular or compact tetraquark models. These two models predict quite different features for the accessible SU(3) multiplets in the scalar and axial-vector sectors.

We performed N_f=3+1 lattice simulations and calculate the energy levels of of the SU(3) [6] and [15] multiplets for both the scalar and axial-vector mesons.
In both sectors we find attractive states for the [6] and repulsive interactions for the [15]. This is consistent with the hadronic molecule picture, but not the compact tetraquark picture a low-lying [15] states in the axial-vector sector but not in the scalar sector.

Speaker: Eric Gregory (Juelich Supercomputing Center)

QCD at nonzero temperature and density

268 Hybrid Charmonium at Finite Temperature

Drawing upon well established zero-temperature techniques, we present, for the first time, insight into the fate of the $1^{-+}$ exotic charmonium state at finite temperature using anisotropic FASTSUM ensembles. Specifically, we use distillation with a wide operator basis which has been extensively used at zero-temperature by the Hadron Spectrum Collaboration to study the charmonium spectrum. The constant contribution to some finite temperature temporal correlation functions requires particular care with the extended operator basis common to distillation setups and we discuss this effect. As an alternative to derivative based extended operators, we also consider the use of optimal distillation profiles at finite temperature for the first time. Finally, we remark on the change to the $1^{-+}$ spectral function via consideration of the reconstructed correlator method.

Speaker: Juan Andres Urrea Nino (Trinity College Dublin)

269 Understanding thermalization of the magnetic gluons in a non-Abelian gauge theory

We demonstrate the chaoticity inherent in SU(2) gauge theory consisting of soft momentum modes both in and out-of-thermal equilibrium conditions using lattice techniques. The non-equilibrium state has been realized starting from an over-occupied initial condition for low momentum soft gluons whereas the thermal state comprises of strongly interacting soft gluons at temperatures where these are well separated from the hard momentum modes. Spectra of positive Lyapunov exponents is observed in both these states, similar to a chaotic dynamical system. From the Kolmogorov-Sinai entropy rate measured in terms of this spectrum, we estimate a typical time-scale of $\sim 0.50(3)$ fm/c to achieve thermalization at $T\sim 600$ MeV starting from the non-thermal state. Next, we have also studied the sphaleron rate in non-Abelian gauge theories both in and out-of-thermal equilibrium conditions. From the time dependent scaling of the sphaleron rate in non-thermal case within self-similar regime, we have estimated the typical thermalization time for the magnetic gluons relevant for e.g. in the context of early universe.

Speaker: Sayak Guin (The Institute of Mathematical Sciences)

270 Spatially inhomogeneous confinement/deconfinement phase transition in accelerated gluodynamics

Quark-gluon plasma created in heavy-ion collision experiments is subjected to huge acceleration which might modify QCD properties. The toy model which allows to study the influence of
acceleration on a strongly interacting system is QCD in the Rindler space. In addition the Rindler space allows to consider QCD properties close to the event horizon of a black hole.
In this report the first results of our study of gluodynamics in the Rindler space are presented. We consider the case of weak acceleration when the system under investigation is far from the event horizon. We found spatially inhomogeneous confinement/deconfinement phase transition.
The space position of this transition can be well described by the Tolman-Ehrenfest law.

Speaker: Victor Braguta (JINR)

271 Spatially inhomogeneous confinement/deconfinement phase transition in rotating QGP

Using first-principle numerical simulations, we find a new spatially inhomogeneous phase in rotating gluon plasma. This mixed phase simultaneously contains regions of both confining and deconfining states in thermal equilibrium. The location of the spatial transition between the two phases is determined by the local critical temperature. We measure the local critical temperature as a function of angular velocity and radius for a full imaginary rotating system and within a local thermalization approximation, and find good agreement between these approaches. An analytic continuation of our results to the domain of real angular frequencies indicates a profound breaking of the Tolman-Ehrenfest law in the vicinity of the phase transition, with the confining (deconfining) phase appearing farther from (closer to) the rotation axis.

Speaker: Artem Roenko (BLTP, JINR)

Quantum computing and quantum information

Convener: Emanuele Mendicelli (University of Liverpool (United Kingdom))

272 Toward Efficient Trotter-Suzuki Schemes for Long-Time Quantum Dynamics

Accurately simulating long-time dynamics of quantum many-body systems—whether in real or imaginary time—is a challenge in both classical and quantum computing due to the accumulation of Trotter errors. While low-order Trotter-Suzuki decompositions are straightforward to implement, their rapidly growing error limits access to long-time observables and ground state properties. I will present a framework for constructing efficient high-order Trotter-Suzuki schemes by identifying their structure and directly optimizing their parameters over a high-dimensional space. This method enables the discovery of new schemes with significantly improved efficiency compared to traditional constructions, such as those by Suzuki and Yoshida. I will demonstrate the effectiveness of these decompositions on the Heisenberg XXZ model, comparing their performance and presenting the newly discovered schemes. Finally, I will discuss ongoing efforts to extend this framework to even higher orders and apply the derived schemes to quantum hardware, pushing the boundaries of both theoretical advancements and practical quantum computing.

Speaker: Marko Maležič (University of Bonn / Helmholtz Institute for Radiation and Nuclear Physics)

273 An analog cold-atom quantum simulator for SU(3) string dynamics

Simulating the real-time dynamics of SU(3) strings is one of the major near-term goals for the quantum simulation community. We propose a protocol for an analog quantum simulation of this non-Abelian physics using cold atoms. Based on the Loop-String-Hadron (LSH) framework, our approach maps the SU(3)-invariant dynamics of strings and hadrons onto an SU(3) ionic Fermi-Hubbard model with three fermionic species, realizable with alkaline-earth-like atoms trapped in an optical lattice. This protocol maintains all local constraints, including the on-site SU(3) and on-link Abelian Gauss laws. We will demonstrate the validity of this approach by comparing the energy spectrum of the analog system with that of the target SU(3) gauge theory at a specific coupling, showing excellent agreement. The proposed simulation is scalable, fully gauge-invariant, and implementable with near-term technology, offering a tangible pathway to experimentally investigate non-perturbative string dynamics.

Speaker: Emil Mathew (BITS Pilani KK Birla Goa Campus)

274 Exponential Improvement in Quantum-Simulation Cost of Lattice Quantum Chromodynamics using Product Formulas

We discuss how a systematic partitioning of the terms in a lattice gauge theory Hamiltonian, with regard to electric-basis discretization, can be done so as to dramatically reduce the number of terms to be simulated in product-formula-based quantum simulation protocols (including Trotterization). Compared to another frequently cited proposal, this simple regrouping can immediately drop at least a factor of one billion from the gate cost of simulating magnetic interactions in the fault-tolerant regime. We estimate about 13 overall orders of magnitude reduction in overall gate cost when other aspects of the cost are taken into consideration. Our findings indicate the maximum potential for product-formula methods is not a settled matter and warrants continued investigation.

Speaker: Jesse Stryker (Lawrence Berkeley National Laboratory)

275 A Quantum Oracle for Constraint Preservation in SU(3) Lattice Gauge Theory Simulations

Quantum simulation of non-Abelian gauge theories like QCD requires an efficient encoding of physical degrees of freedom that respects gauge invariance. The Loop-String-Hadron (LSH) formulation offers a promising path, significantly reducing the number of qubits required to represent the SU(3) invariant states in 1+1 dimensions compared to traditional approaches. While the LSH basis automatically satisfies the non-Abelian Gauss laws, remnant local constraints on flux numbers must still be upheld. During time evolution on noisy quantum hardware, errors can accumulate, taking the system out of the valid physical Hilbert space. To address this, we present the construction of a quantum oracle designed to check these local constraints on the qubit register. This talk will detail the LSH mapping for SU(3) and the design of the constraint-checking oracle. We will present a resource analysis, quantifying the costs in terms of qubit count, gate operations, and circuit depth, providing a crucial tool for error mitigation in future quantum simulations of QCD.

Speaker: Fran Ilcic (BITS Pilani, KK Birla Goa Campus)

Quark and lepton flavor physics

Convener: Alejandro Vaquero Avilés-Casco (University of Zaragoza)

276 $K\pi$ Scattering as a Step Towards $B \to K^* \ell^+ \ell^-$ from Lattice QCD

The study of rare semileptonic $B$ decays such as $B \to K^* \ell^+ \ell^-$ offers a sensitive probe of the Standard Model and potential new physics, but a key theoretical challenge for lattice QCD is the treatment of the resonant $K^*$ in the final state. Traditional calculations rely on the narrow-width approximation, treating the $K^*$ as stable. In this talk, I present first steps towards going beyond this approximation by studying $K\pi$ scattering on an RBC/UKQCD ensemble and extracting information about the $P$-wave channel relevant to the $K^*$. I will discuss the methodology, show initial results for the finite-volume spectrum and phase shift, and outline the path toward determining $B \to K\pi$ matrix elements in a fully dynamical framework.

Speaker: Felix Benjamin Erben

277 Kaon radiative leptonic decay rates from Twisted Mass simulations at the physical point

We present our recent calculation of radiative leptonic decay
rates of the kaon, based on twisted clover simulations at the physical
point carried out by ETM collaboration. The calculation improves
substantially our previous estimate, by improving the stastistcs,
including electrounquenched diagrams, carrying out the continuum
extrapolation on three different lattice spacings and investigating the
finite volume correction with two different volumes. We discuss the
phenomenological relevance of the calculation, and future direction of
research.

Speaker: Francesco Sanfilippo (INFN Roma Tre)

278 An Update on the Isospin-Breaking Effects in the Pion Decay Constant with Staggered Quarks

We present an update of the ongoing computation of the isospin-breaking effects in the Pion Decay Constant from the BMW Collaboration. The calculation is carried out with N$_f$=2+1+1 staggered quarks with a near-physical pion mass and QED$_L$. We present some preliminary results of the valence-valence contribution to the axial-pseudoscalar correlator for different volumes $L=4.2, 6.3, 8.4$ fm at $a=0.1315$ fm and a single volume $L=6$ fm and at $a=0.0952$ fm. We also discuss the next steps and plans.

Speaker: Alessandro Cotellucci (Forschungszentrum Jülich)

279 Renormalized quark masses using gradient flow

We propose a new and simple method for determining the renormalized quark masses from lattice simulations. Renormalized quark masses are an important input to many phenomenological applications, including searching/modeling physics beyond the Standard Model. The non-perturbative renormalization is performed using gradient flow combined with the short-flow-time expansion that is improved by renormalization group (RG) running to match to the $\overline{\text{MS}}$-scheme. RG running connects the lattice scale to higher energies thus improving the$\overline{\text{MS}}$-scheme matching. Implementing the RG running perturbatively, we demonstrate this method works reliably at least up to the charm-quark mass and is not exhibiting any signs of the usual "window problem".
Using RBC/UKQCD's (2+1)-flavor Shamir domain-wall fermion ensembles with Iwasaki gauge action, we find $m_s^{\overline{\text{MS}}}(\mu=2\text{ GeV}) = 89.1(3.2)$ MeV and $m_c^{\overline{\text{MS}}}(\mu=3 \text{ GeV}) = 973.4(8.3)$ MeV. These results predict the scale-independent ratio $m_c/m_s= 12.1(4)$.
Generalization to other observables is possible, providing an efficient approach to determine non-perturbatively renormalized fermionic observables like form factors or bag parameters from lattice simulations.

Speaker: Oliver Witzel (Universität Siegen)

Structure of hadrons and nuclei

Convener: Christopher Monahan

280 Quark mass dependence of higher-twist in nucleon structure functions

Higher-twist effects reflect the physics of quark-quark and quark-gluon correlations that provide unique insights into the dynamics inside hadrons that goes beyond the parton model. These effects are sub-leading (suppressed by powers of $1/Q^2$) but crucial for quantitative analyses and precision tests of QCD. By their nature higher-twist contributions are non-perturbative. In this contribution, we report on QCDSF Collaboration's calculations of the Compton amplitude on 2+1-flavour ensembles with varying quark masses corresponding to $m_\pi = [410, 360, 300, 265]$ MeV, at a fixed volume of $V=48^3 \times 96$ and coupling $\beta = 5.65$ ($a = 0.068(3)$ fm). By extracting the lowest even isovector moment of the nucleon $F_2$ structure function, we quantify the quark mass dependence of the higher-twist effects. Our preliminary results indicate a significant quark mass dependence towards the low-$Q^2$ ($\sim 1 \; {\rm GeV}^2$) region.

Speaker: Dr K. Utku Can (The University of Adelaide)

281 Lattice extraction of the Collins-Soper kernel using the auxiliary field representation of the Wilson line

The Collins-Soper (CS) kernel may be obtained through the TMD soft function by formulating the Wilson line in terms of 1-dimensional auxiliary fermion fields on the lattice. Our computation takes place in the region of the lattice that corresponds to the “spacelike” region in Minkowski space, i.e., Collins' scheme. We explore two methods for obtaining the CS kernel. The "ratio method"; which would allow us to obtain the soft function as well as the CS kernel. And the "double ratio"; which allows us to achieve a high degree of statistical precision, but only produces the CS kernel.The matching of our result to Minkowski space is achieved through the mapping of the auxiliary field directional vector to the Wilson line rapidity. I present a preliminary extraction of the CS kernel using the ``double ratio", and discuss the methodology employed.

Speaker: Wayne Morris (National Yang Ming Chiao Tung University)

282 Lattice QCD Frontiers in TMD Physics

Transverse-momentum-dependent parton distributions (TMDs) are essential for unraveling the three-dimensional structure of hadrons, forming a core scientific component of the Electron-Ion Collider (EIC) program. Employing a novel Coulomb-gauge-fixed lattice QCD approach at physical quark masses, we reliably access transverse separations up to approximately 1 fm, corresponding to the small transverse momenta relevant for EIC measurements. In this presentation, we summarize recent lattice QCD advancements, systematically progressing from foundational calculations of the Collins-Soper (CS) kernel to detailed studies of pion and proton TMD structures. Our calculations include a first-principles determination of the nonperturbative CS kernel, crucial for describing the rapidity evolution of TMDs. Extending these methodologies, we investigate pion valence-quark TMD distributions, providing new insights into the internal transverse structure of the pion. Most significantly, our benchmark computations for proton helicity and flavor-dependent unpolarized TMDPDFs reveal similarities in transverse dependence between helicity and unpolarized distributions at moderate momentum fractions, alongside discernible flavor-dependent variations. Collectively, these lattice results pave the way, for the first time, toward direct QCD-based comparisons and serve as essential guidance for phenomenological parametrizations derived from global analyses of experimental data.

Speaker: Swagato Mukherjee

283 Extracting Collins-Soper Kernel from Transverse-momentum-dependent Wave Functions on Lattice QCD

We present a lattice QCD calculation of the Collins-Soper kernel, which governs the rapidity evolution of transverse-momentum-dependent (TMD) distributions, using Large Momentum Effective Theory (LaMET). Quasi-TMD wave functions are computed with three meson momenta on CLQCD configurations (multiple lattice spacings) employing clover quarks and varied hadronic states. HYP smearing is applied to staple-shaped gauge links and Wilson loops to enhance signal-to-noise ratios. Divergences are systematically addressed: linear divergences via Wilson-line renormalization and logarithmic divergences through a self-renormalization-inspired scheme.

By combining two-loop light-cone matching, renormalization group evolution, and leading renormalon resummation, we determine the Collins-Soper kernel for transverse separations up to 1 fm, with extrapolation to large-momentum and continuum limits. This work provides critical inputs for soft functions and precision studies of TMD physics, advancing first-principles QCD in high-energy phenomenology.

Speaker: ZHICHAO GONG (Shanghai Jiao Tong University)

Theoretical developments and applications beyond Standard Model

Convener: Navdeep Dhindsa

284 Symplectic Quantization: Disclosing the Deterministic Framework Behind Quantum Mechanics

We present Symplectic Quantization, a novel functional approach to quantum field theory that allows us to sample quantum fluctuations directly in Minkowski space–time, bypassing the limitations of traditional importance sampling techniques restricted to imaginary time. Our method is based on a deterministic dynamics governed by Hamilton-like equations in an auxiliary time parameter $\tau$. We show that the microcanonical correlation functions are equivalent to those generated by a Minkowskian canonical theory where quantum fields fluctuations are weighted by the factor $exp(iS/\hbar)$, $S$ being the original action of the system. We benchmark the approach on the quantum harmonic oscillator, where we are able to reconstruct the full real-time dynamics, not only of the ground state but also of excited states and superpositions. The method reproduces quantum expectation values with high accuracy and captures interference effects that are inaccessible to Euclidean formulations. These results demonstrate that our framework can recover the complete structure of quantum mechanics in real time, establishing a solid foundation for applications to interacting quantum field theories.

Speaker: Martina Giachello (Gran Sasso Science Institute)

285 Symplectic Quantization : Disclosing the Deterministic Framework Behind Quantum Field Theory}

We introduce Symplectic Quantization, a functional approach to quantum field theory that samples quantum fluctuations directly in Minkowski space–time, bypassing the traditional importance sampling techniques that are restricted to imaginary-time. Our method evolves fields via deterministic Hamilton-like equations in an auxiliary time parameter $\tau$. We prove that the microcanonical correlation functions are equivalent to those generated by a Minkowskian canonical theory where quantum fluctuations are weighted by the factor $\exp(iS/\hbar)$, $S$ being the original action of the system. As a benchmark we study a free scalar field theory in $1+1$ dimensions, where we are able to reconstruct the full real-time dynamics of the Feynman propagator. We also recover the Schwinger–Dyson equations, including contact terms, clarifying the role of the generalized Hamilton equations within this framework. These results demonstrate that our framework can recover the complete structure of free quantum field theory in real time, establishing a solid foundation for applications to interacting quantum field theories.

Speaker: Francesco Scardino (Università di Roma "La Sapienza")

286 A novel framework for spectral density reconstruction via quadrature-based Laplace inversion

In this work, we explore a numerical approach to performing the inverse Laplace transformation, with an emphasis on stability and robustness under noisy conditions. Our quadrature-based method integrates reparameterization, data smoothing, optimization techniques, and various approaches to regularizing ill-conditioned systems. Together, these elements enable consistency checks that enhance the reliability of the inversion process. Through a series of controlled tests on toy models, we demonstrate the stability and effectiveness of the method in the presence of noise. Using mock data, we approximate spectral densities from Euclidean correlators, generating smoothed and stable results that accurately reproduce correlator behavior; particularly at large Euclidean times. We also briefly explore the application of this framework to actual lattice simulations. Finally, we discuss possible directions for extending this approach to a broader class of problems in Lattice QCD and theoretical physics, where the inverse Laplace transformation is typically ill-posed.

Speaker: Demetrianos Gavriel (University of Parma, INFN Parma)

287 Discretization effects of gradient flows in QCD-like theories on the lattice

Recent software advances now allow large-scale lattice studies of the Corrigan–Ramond large-$N_c$ limit of Yang-Mills theory coupled with a two-index antisymmetric fermion, providing a path to SUSY Yang-Mills. We are currently generating ensembles for $N_c=4,5,6$ for lattice spacings in the range $0.1 - 0.08 \,\mathrm{fm}$, enabling a careful study of cutoff effects and lattice topological properties to properly monitor freezing. In particular, in this talk, we explore the topological properties of such gauge configurations, where fractional charges might naively be expected. Using a gluonic definition of the topological charge combined with gradient flow, we perform an analysis of the effect of different discretisations of the kernel action, from which we identify and interpret quantitative differences between Wilson and over-improved flows (such as DBW2), showing how these are mitigated in the continuum limit.

Speaker: Pietro Butti (Quantum Theory Center, IMADA and D-IAS, University of Southern Denmark)

288 Probing Loop Dynamics in 2+1-Dimensional SU(2) Lattice Gauge Theory via GPU-Accelerated Exact Diagonalization

Simulating the real-time dynamics of non-Abelian lattice gauge theories in more than 1+1 dimensions presents a significant computational challenge. We present an exact diagonalization study of 2+1-dimensional SU(2) lattice gauge theory, leveraging the gauge-invariant Loop-String-Hadron (LSH) framework. By harnessing GPU-based computation, we have successfully pushed the classical simulation frontier to systems of up to 16 plaquettes. This talk will detail our computational strategy and present the first results on the real-time evolution of electric flux loop dynamics within the pure gauge sector. Our work provides crucial benchmarks for near-term tensor network simulators as well as quantum simulators and opens a new avenue for studying fundamental phenomena like thermalization directly from the Hamiltonian perspective in higher dimensions.

Speaker: Ms Aahiri Naskar (BITS Pilani Goa K K Birla Campus)

Saturday 8 November

Plenary session

Convener: Masafumi Fukuma (Kyoto University)

289 Hamiltonian Formalisms of Lattice Gauge Theories

For decades, the lattice community has successfully extracted fundamental properties of non-abelian gauge theories, like QCD, using the Euclidean path integral formalism and Monte Carlo methods. However, the advent of quantum computation, quantum simulation, and advanced tensor network methods has created new opportunities and demands for a Hamiltonian approach, which is better suited for describing real-time dynamics and operating directly on states belonging to the physical Hilbert space.
In this talk, we review some of these recently developed formalisms that are of active interest to the lattice community. Following this overview, we provide a detailed exposition of the Loop-String-Hadron (LSH) framework and demonstrate how LSH reformulates the theory in an explicitly gauge-invariant basis of electric flux loops and open strings connecting matter fields, which naturally map to hadronic states. This choice of basis offers a physically intuitive and computationally efficient Hilbert space truncation. We also highlight its direct applications, highlighting how eliminating redundant gauge degrees of freedom makes exact diagonalisation and tensor network calculations feasible to study real-time dynamics, provide insights about thermalization properties, enable mapping of physical degrees of freedom on analog and digital quantum hardware - followed by quantum simulation of dynamics. We will also present how the basis more effectively captures the entanglement structure of the theory.

Speaker: Indrakshi Raychowdhury

290 Renormalization group on tensor networks

Tensor networks provide novel formulations of lattice field theories, which in turn enable the development of practically efficient renormalization group methods. Unlike conventional Monte Carlo methods, tensor networks are free from the sign problem in principle and can be straightforwardly extended to fermionic systems. We present recent progress in these formulations and numerical renormalization group methods, and discuss the roadmap toward their application to QCD.

Speaker: Shinichiro Akiyama (University of Tsukuba)

291 Variance-reduction algorithms for lattice QCD

A significant component of the cost of making physical predictions from lattice QCD stems from the computation of correlation functions on a fixed ensemble of gauge fields. This cost is highly dependent on the observable of interest and the details of its representation, including any approximation needed to estimate it, aside from the sampling algorithm used for the fields. Moreover, the variance of such estimators may depend strongly on physical parameters such as the lattice spacing and volume, which gives an important insight into the cost of reaching the relevant physical limits. In this talk, I will review some observables involving quark propagators, in particular quark connected and disconnected diagrams, and discuss variance-reduction schemes based on decompositions of the propagators. Such strategies have already proven useful for precision physics observables and in future may help reduce the computational cost of approaching large volumes.

Speaker: Tim Harris

11:00 Coffee break

Plenary session

Convener: Zohreh Davoudi (University of Maryland)

292 Status of Compositeness for New Physics from the Lattice

Special classes of non-supersymmetric, strongly interacting gauge theories provide ultraviolet completions for new physics extensions of the Standard Model that offer potential solutions to key open problems in the energy frontier, including the absence of new physics signatures at energies just above the electroweak scale, the anomalously heavy mass of the top quark, the absence of new flavor changing neutral current interactions, and the origin of dark matter. The non-perturbative nature of these theories makes lattice field theory the natural tool for computing the associated physical observables. After a brief overview of widely-studied proposals for strongly coupled theories in the context of beyond the Standard Model physics, in this talk, I focus on Higgs compositeness and top partial compositeness. Primarily, I discuss the Sp(4) gauge theory with matter consisting of two fundamental and three antisymmetric fermions, detailing its motivations as a template for this class of models. I present recent results from the TELOS collaboration on the mass spectrum of the model, emphasizing methodological advances that have broader applicability to lattice QCD studies. Finally, I discuss finite-temperature calculations in Sp(4) gauge theories with and without fermionic matter, and the potential relevance of associated phase transitions as sources of a stochastic relic density of gravitational waves.

Speaker: Biagio Lucini (Queen Mary University of London (UK))

293 Three-particle scattering amplitudes from lattice QCD

I review recent progress in calculating scattering amplitudes and resonance properties involving three particles using lattice QCD results for the finite-volume spectrum, coupled with solutions to the associated integral equations. I describe the outlook for future extensions of this work.

Speaker: Stephen Sharpe (University of Washington)

294 Lattice 2026

13:00 Lunch break

Event ends