Welcome by the APCTP President

• Misao Sasaki (Asia Pacific Center for Theoretical Physics (APCTP))

Room: 503

Presentation of INPP "Demokritos"

• Christos Markou (INPP)

Room: 503

KM3NeT: Neutrino telescopy in the abyss

• Christos Markou (INPP)

Room: 503 The KM3NeT Collaboration is incrementally building two underwater Cherenkov neutrino telescopes in the Mediterranean Sea. Both telescopes share the same technology for neutrino detection, by studying Cherenkov radiation from secondary charged particles produced in neutrino interactions. Photomultipliers are a common choice for the detection of Cherenkov radiation, but the hostile underwater environment, affected by sea currents and bioluminescence demands innovative solutions in KM3NeT. The KM3NeT design is modular and allows for data taking with the telescope still in the construction stage. Early technical and scientific results are enticing. In particular, KM3NeT recently discovered a neutrino of unprecedented energy from outer space. The speaker will cover KM3NeT telescope design and operation, as well as give a brief overview of the latest results.

Thermodynamics of various black holes

• Bum-Hoon Lee (Sogang)

Room: 503 After the motivation for the extended gravity, such as higher curvatures beyond Einstein, various thermodynamic black holes will be studied. Black holes, with their fundamental structure, play a crucial role in guiding us towards the quantum domain. Their thermodynamic properties across different theories, particularly through holography, will be examined with the negative cosmological constant considered mostly. The theory with the Gauss-Bonnet term will also be mentioned. A notable feature of dilaton-Einstein-Gauss-Bonnet gravity in 4 dimensions, unlike Einstein's gravity, is the presence of a minimum mass threshold below which a black hole cannot form. Phase diagrams for various black holes will be treated.

Finite landscape of 6d N=(1,0) supergravity

• Hee-Cheol Kim (POSTECH)

Room: 503

Near-extremal dynamics away from the horizon

• Ioannis Papadimitriou (U. of Athens)

Room: 503 Near-extremal black holes are usually studied by zooming into the throat that describes their near-horizon geometry. Within this throat, one can argue that two-dimensional JT gravity is the appropriate effective theory that dominates at low temperature. Here, we discuss how to capture this effective description by standing far away from the horizon. Our strategy is to construct a phase space within gravitational theories in AdS$_{d+1}$ that fixes the radial dependence while keeping the transverse dependence arbitrary. This allows us to implement a decoupling limit directly on the phase space while keeping the coordinates fixed. With this, we can relate the effective description in JT gravity to the CFT$_d$ description at the boundary of AdS$_{d+1}$, which we do explicitly in AdS$_3$ and non-rotating configurations in AdS$_4$. From the perspective of the dual CFT, our decoupling limit should be understood as a flow between a CFT$_{d}$ and a near-CFT$_1$. Our analysis shows that local counterterms can be constructed in the near-CFT$_1$, which arise from the anomalies (or absence of them) in the CFT$_{d}$. We show that one of these counterterms is the Schwarzian effective action, making this sector a scheme-dependent choice. This illustrates the delicate interplay between a far and a near analysis of near-extremal black holes.

Supersymmetric localization of N=(2,2) theories on a spindle

• Imtak Jeon (Huzhou U.)

Room: 503 We consider two-dimensional N=(2,2) supersymmetric field theories living on a weighted projective space WCP$_{[n_1,n_2]}^1$, often referred to as a spindle. Starting from the spindle solution of five-dimensional minimal gauged supergravity, we construct a theory on a spindle which preserves supersymmetry via the anti-twist mechanism and admits two Killing spinors of opposite R-charge. We apply the technique of supersymmetric localisation to compute the exact partition function for a theory consisting of an abelian vector multiplet and a chiral multiplet, finding that the path integral localises to a real moduli space of vector multiplet fluctuations. We compute the one-loop determinants via the equivariant index, using both the method of unpaired eigenvalues and the fixed point theorem, finding agreement between the two approaches. We conclude with the explicit partition function for an example of a charged chiral multiplet in the presence of a Fayet-Iliopoulos term and comment on its dependence on the overall length scale of the geometry. This work paves the way towards uncovering two-dimensional dualities, such as mirror symmetry, for field theories defined on orbifold backgrounds.

Einstein gravity with cosmological constant and scalar fields is nonperturbatively renormalizable

• Nobuyoshi Ohta (Kinki University)

Room: 503

ER=EPR and strange metal from field theory wormhole.

• Sang-Jin Sin (Hanyang U.)

Room: 503 We give an understanding how strange metals arise from the spatially random Yukawa-SYK model based on the wormhole picture and find a parallelism between the disorder theory and quantum gravity. We start from the observation that the Gaussian average over the spatial random coupling gives a wormhole, defined as a mechanism for long range interaction without causal suppression outside the lightcone. We find that the large- N limit equivalence of the quenched and annealed averages provides a field theory version of the ER=EPR. Since the wormhole establishes momentum exchanges over arbitrary distance without causal suppression, it provides a mechanism of the planckian dissipation. It also tells us why SYK-like models describe strongly interacting systems even in the small coupling case. We classify the disorder samples into two classes: I) spatially random coupling with wormholes and no information loss, II) spatially uniform coupling with decoherence.

Dual holography from a non-perturbative generalization of the Wilsonian RG framework

• Ki-Seok Kim (POSTECH)

Room: 503 In my opinion, physics is to aim understanding the macroscopic universal IR physics from the microscopic individual UV physics based on the first principle. The Wilsonian renormalization group (RG) framework would be the first organization principle. Unfortunately, this theoretical framework has its limitation in describing many long-standing physics problems, where the RG flow from UV to IR is nonperturbative in nature and beyond the paradigm of spontaneous symmetry breaking. In this talk, we discuss how to generalize the Wilsonian RG framework in a nonperturbative way. First, we introduce a brute-force way of RG transformations. Remarkably, the resulting Wilsonian effective action contains a particular class (most singular) of quantum corrections in the all-loop order, not exact but completely nonperturbative in nature. We confirm this nonperturbative physics explicitly from the Kondo problem, which shows the asymptotic freedom (decoupled local moment fixed point) at UV and confinement (local Fermi liquid fixed point) at IR. Although this brute-force way of RG transformations is explicit, the intermediate procedure looks dirty and hidden, involved with the heat-kernel calculation in a general background. We realize that there exists a topological structure in this brute-force construction. Second, we discuss an elegant reformulation of the previous nonperturbative RG theoretical framework, referred to as a cohomological-type topological field theory construction a la Witten. We demonstrate that this topological reformulation is essentially the same as the previous explicit derivation. Interestingly, we observe that this cohomological construction gives a deep connection to the path integral representation of the exact functional RG equation, where the RG flow of the probability distribution function is governed by the Fokker-Planck-type equation. Based on this novel reformulation, we discuss Weyl anomaly inflow and cancellation for the resulting renormalized effective action, regarded to be the consistency equation for the nonperturbative RG flow description. We see that all these mathematical structures are consistent with the holographic duality conjecture.

Emergent factorization of Hilbert space at large-N and black holes

• Junggi Yoon (Kyung-Hee)

Room: 503

Magnetogenesis via plasma processes

• Young Dae Yoon (Asia Pacific Center for Theoretical Physics)

Room: 503 Spontaneous magnetic field generation, or magnetogenesis, is an important process in both cosmological and astrophysical contexts. In plasma physics, it is well known that dynamo processes can amplify a given magnetic field, but how the required seed magnetic field is spontaneously generated is relatively less understood. Here I present via analyzing the equation of motion of a magnetized fluid that a term due to the pressure tensor is responsible for seed magnetogenesis in a collisionless plasma. In relativistic regimes, there is an additional term due to a non-commutative relationship between momentum and velocity that further affects magnetogenesis.

Emergence of Meron Kekulé lattices in twisted Néel antiferromagnets

• Kyoung-Min Kim (Asia Pacific Center for Theoretical Physics)

Room: 503 In magnetic materials, topological solitons, such as merons, are often discovered as lattice elements within Bravais lattice structures. In this talk, we will present an intriguing alternative: in twisted bilayer antiferromagnets, merons can form an exotic, distorted non-Bravais lattice structure known as a Kekulé lattice. Specifically, we will demonstrate that the spatial modulation of interlayer coupling through moiré patterns stabilizes the meron cores into the Kekulé-O pattern, which features different intracell and intercell bond lengths across the moiré supercells, thereby forming a Meron Kekulé lattice. Furthermore, we will show that the two bond lengths of the Meron Kekulé lattice can be finely tuned by adjusting the twist angle and specifics of the interlayer exchange coupling, indicating extensive control over the meron lattice configuration compared to conventional magnetic systems. Lastly, we will discuss the fascinating future research outlook of how bond-dependent interactions of merons affect phonon-like collective excitation modes associated with their core vibrations.

An introduction to non-Hermitian physics

• Zhesen Yang (APCTP)

Room: 503 This talk provides an introduction to non-Hermitian physics, covering key consequences of non-Hermitian Hamiltonians such as complex eigenvalues, nonorthogonal eigenstates, and the non-Hermitian skin effect (NHSE). It presents our contributions to non-Hermitian topological band theory, including clarifying topological charges of exceptional points and classifying 3D exceptional line semimetals, as well as advancements in non-Bloch band theory like establishing the bulk-boundary correspondence between spectral winding number and NHSE and proposing dynamical degeneracy splitting. Additionally, the talk discusses experimental realizations and physical understandings of NHSE, and outlines future directions in non-Hermitian many-body theory with a call for collaborators.

Phase transitions and domain walls with holography-inspired hydrodynamics

• Matti Jarvinen

Room: 503 Studying phase transitions and domain walls using the gauge/gravity duality typically leads to challenging tasks in numerical gravity. However, such tasks can be dramatically simplified by considering hydrodynamics matched to the holographic model. In this talk, I discuss extended hydrodynamics (perfect fluid hydrodynamics plus a scalar, i.e. the order parameter of the transition) fitted to data from the holographic Witten model to study the physics of phase transitions. Among other things, we find a simple formula for the velocity of moving walls and surprising behavior of hot plasma remnants in the last stages of the transition in an expanding setup.

Logarithmic corrections to near-extremal entropy of de Sitter black holes

• Debangshu Mukherjee (Asia Pacific Center for Theoretical Physics (APCTP))

Room: 503 I will briefly review logarithmic corrections to black hole entropy. Following that, I will focus on thermodynamics of de Sitter black holes and our recent work (https://arxiv.org/abs/2503.08617) on log T corrections to the entropy of de Sitter black holes. I will establish the result that at leading order, the small temperature corrections to the extremal entropy is universal in the cold and Nariai limit, paving the way for similar such computations and tests in higher dimensional dS black hole spacetimes, including rotating dS black holes.

Holographic realms of quantum electrodynamics

• Kostas Filippas (NCSR Demokritos, Institute of Nuclear and Particle Physics)

Room: 503 We recently proposed a holographic duality between massive theories in 4D flat spacetime and massless ones on its conformal (lightlike) boundary, where Poincare maps to conformal symmetry. The dual boundary space is really the conformal class of $\mathbb{S}^2\times\mathbb{R}$ cylinders, which is also the conformal (timelike) boundary of AdS$_4$. This leads to a triality between three holographic realms $-\mathbb{R}^4$, $\mathbb{S}^2\times\mathbb{R}$ and AdS$_4-$ all supporting equivalent particle theories. As an illustration, we match the path integrals for free fermions across all three realms. We then identify the Landau levels of the $\mathbb{R}^4$ realm with a monopole problem on the cylinder, and with the spectrum of an extremal magnetic black hole in the AdS$_4$ realm. Finally, we suggest that QED with $N_f$ flavors of fermions is dual to an Abelian Chern-Simons-matter theory coupled to $2N_f$ massless fermions on the boundary, which in turn should be dual, for large $N_f$, to a higher-spin theory in AdS$_4$.

Dimer, cluster, and supersymmetric guage theories

• Norton Lee (IBS-CGP)

Room: 503

Matter coupled Aristotelian gravity

• Patricio Salgado-Rebolledo (Asia Pacific Center for Theoretical Physics (APCTP))

Room: 503 We consider matter couplings to Aristotelian gravity with arbitrary $p$-brane foliations. To this end, we extend the $p$-brane Aristotelian algebra by including a dilatation symmetry generator that acts anisotropically on the longitudinal and transverse directions. Using this conformal extension, we demonstrate how Aristotelian gravity can be coupled to quadratic-derivative matter models, as well as to certain higher-derivative models recently studied in connection with fractons. Finally, we briefly review a recently proposed effective description of multi-Weyl semimetals based on string-foliated Aristotelian geometry.

A test of Einstein’s equivalence principle in future VLBI observations

• Susmita Jana (Asia Pacific Center for Theoretical Physics (APCTP))

Room: 503 We show that very-long-baseline-interferometry (VLBI) observations of supermassive black holes will allow us to test the fundamental principles of General Relativity (GR). GR is based on the universality of gravity and Einstein’s equivalence principle (EEP). However, EEP is not a basic principle of physics but an empirical fact. Non-minimal coupling (NMC) of electromagnetic fields violates EEP, and their effects manifest in the strong-gravity regime. Hence, VLBI observations of black holes provide an opportunity to test NMC in the strong-gravity regime. To the leading order in the spin parameter, we explicitly show that the NMC of the electromagnetic field introduces observable modifications to the black hole image. In addition, we find that the size of the photon rings varies by ∼ 3rH, which corresponds to ∼ 30μas for Sagittarius A∗ and ∼ 23μas for M87. VLBI telescopes are expected to attain a resolution of ∼ 5μas in the near future. However, direct detection of the photon ring will require the resolution of ∼ 1μas for M87, which can potentially be probed by the space-based Event Horizon Explorer.

Dynamical aspects of analogue gravity

• Kunal Pal (Asia Pacific Center for Theoretical Physics (APCTP))

Room: 503 The primary motivation behind the analogue gravity programme is the experimental simulation of fundamental features of field quantisation in curved spacetimes, which are typically impossible to detect in real gravitational fields. The analogue gravity idea of William Unruh has led to the first observations of phenomena related to the paradigmatic quantum Hawking effect in the experimentally realisable physical system, Bose-Einstein condensate (BEC), an ultracold quantum gas of interacting bosons by the Steinhauer group. However, the standard paradigm of analogue gravity only focuses on the kinematical aspect of gravity, the dynamics of fields on a given curved background, not the dynamics of the background itself. In the present talk, I will present a recent approach of our group, where we proposed a coupled background and fluctuation model in the number-conserving approach of BEC, thereby enabling a dynamics of the background itself. I will particularly discuss how the background dynamics are governed by an emergent scalar field theory of gravity, and how the renormalised background may affect the Hawking radiation in a black hole analogue model.

Perturbative solutions of Einstein’s equations: recursive techniques and multipole expansions

• Tabasum Rahnuma (Asia Pacific Center for Theoretical Physics (APCTP))

Room: 503 Perturbative approaches to gravity, particularly within the post-Minkowskian (PM) expansion, provide a powerful framework for studying gravitational interactions beyond the weak-field limit. In this talk, I will highlight the role of off-shell recursion relations—formulated through the Perturbiner expansion—in systematically organizing gravitational perturbations. These recursive structures naturally generate all orders in Newton’s constant, offering new insight into both conservative dynamics and dissipative effects. Compared to conventional Feynman diagram methods, the Perturbiner approach offers a far more efficient, computer-friendly framework for perturbative gravity, acting as a generating functional for off-shell currents in both gauge and gravity theories. By combining recursive structures with iterative loop integrals, this method transforms the overwhelming complexity of perturbative gravity into a systematic and tractable procedure. This talk will be of interest to researchers in perturbative gravity, self-force dynamics, scattering amplitudes, quantum field theory, and mathematical physics, as well as those interested in computational methods for high-energy theory.

Progress towards numerical two-loop integrand reduction

• Giuseppe Bevilacqua (NCSR Demokritos)

Room: 503 We present a method for the integrand-level reduction of two-loop helicity amplitudes in both d=4−2ϵ and d=4 dimensions. The amplitude is expressed in terms of a set of Feynman integrals and their coefficients that depend on the external kinematics. The method presented in this talk, in conjunction with the ongoing development of the computational framework HELAC-2LOOP, paves the road for the construction of an automated program for numerical two-loop amplitude calculations.

QCD scattering amplitudes at the precision frontier

• Heribertus Bayu Hartanto (Asia Pacific Center for Theoretical Physics (APCTP), Pohang, South Korea)

Room: 503 I will discuss recent progress in the computation of scattering amplitudes required for precision phenomenology at the LHC. I will focus on one of the LHC's precision calculation frontiers: two-to-three scattering process at Next-to-Next-to-Leading Order QCD accuracy. I will review the modern framework to compute two-loop five-particle scattering amplitudes and discuss new results obtained for W+2 photons and H+bb full colour amplitudes.

Miura operators as R-matrices from M-brane intersections

• Saebyeok Jeong (IBS-CGP)

Room: 503

In-out formalism for one-loop effective actions in QED and gravity

• Sang Pyo Kim (Kunsan National University)

Room: 503 The in-out formalism is a systematic and powerful method for finding the effective actions in an electromagnetic field and a curved spacetime provided that the field equation has explicitly known solutions. The effective action becomes complex when pairs of charged particles are produced due to an electric field and curved spacetime. This may lead to a conjecture of one-to-one correspondence between the vacuum polarization (real part) and the vacuum persistence (imaginary part). We illustrate the one-loop effective action in a constant electric field in a Minkowski spacetime and in a uniform electric field in a two-dimensional (anti-) de Sitter space.

Pair production in charged black holes: Monodromy approach

• Chiang-Mei Chen (National Central University)

Room: 503 In this talk I will firstly review the Schwinger effect in charged black holes and then introduce a remarkable alternative approach by using the monodromy. The explicit elaboration of monodromy and the model calculations seem to reveal evidence that the monodromy can provide a practical technique to study the spontaneous pair production in general black holes and electromagnetic fields.

Stochastic thermodynamics of biological systems

• Hyeong-Tark Han (POSTECH)

Room: 503

Statistical physics-informed analysis of fluctuations across scales: from living to astrophysical systems

• Athokpam Langlen Chanu (Asia Pacific Center for Theoretical Physics (APCTP))

Room: 503