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

Session

Quark and lepton flavor physics

5 Nov 2025, 09:00

Homi Bhabha Auditorium (TIFR Mumbai)

Conveners

Quark and lepton flavor physics

• Steven Gottlieb (Indiana University)

Quark and lepton flavor physics

• Andrew Lytle

Quark and lepton flavor physics

• Francesco Sanfilippo (INFN Roma Tre)

Quark and lepton flavor physics

• Teseo San Jose (University of Edinburgh)

Quark and lepton flavor physics

• Alejandro Vaquero Avilés-Casco (University of Zaragoza)

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

Alejandro Saez Gonzalvo (IFIC UV-CSIC)

05/11/2025, 09:00

Talk

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...

184. Isospin-breaking contributions to \varepsilon’ from lattice QCD

Erik Lundstrum (Columbia University)

05/11/2025, 09:20

Talk

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...

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

Ramón Merino (Universidad de Granada)

05/11/2025, 09:40

Talk

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...

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

Matteo Di Carlo (CERN)

05/11/2025, 10:00

Talk

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...

212. Nevanlinna-Pick interpolation from inexact data

Sarah Fields (Columbia University)

05/11/2025, 10:50

Talk

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. ...

153. Non-perturbative Weak Physics using the FMS Mechanism

Sofie Martins (University of Graz)

05/11/2025, 11:10

Talk

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...

133. Electromagnetic pion mass splitting using PV-regulated photon propagator

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

05/11/2025, 11:30

Talk

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...

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

Ahmed Elgaziari (University of Southampton)

06/11/2025, 14:30

Talk

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...

155. Real radiative decays of heavy pseudoscalar mesons

Teseo San Jose (University of Edinburgh)

06/11/2025, 14:50

Talk

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...

164. Inclusive semileptonic decays of heavy mesons from lattice QCD

marco garofalo (University of Bonn, HISKP)

06/11/2025, 15:10

Talk

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...

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

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

06/11/2025, 15:30

Talk

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 =...

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

Francesca Margari (University of Rome Tor Vergata)

06/11/2025, 15:50

Talk

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...

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

Andreas Konstantinou (University of Cyprus)

06/11/2025, 16:10

Talk

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...

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

William Jay (Colorado State University)

07/11/2025, 14:30

Talk

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 $B\to\pi\ell\nu$.

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

Akhil Chauhan (University of Illinois Urbana Champaign)

07/11/2025, 14:50

Talk

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...

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

Anastasia Boushmelev (University of Siegen)

07/11/2025, 15:10

Talk

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....

71. Heavy Meson Lifetimes from Gradient Flow

Matthew Black (University of Edinburgh)

07/11/2025, 15:30

Talk

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...

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

Alejandro Vaquero Avilés-Casco (University of Zaragoza)

07/11/2025, 15:50

Talk

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...

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

Felix Benjamin Erben

07/11/2025, 16:40

Talk

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...

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

Francesco Sanfilippo (INFN Roma Tre)

07/11/2025, 17:00

Talk

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...

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

Alessandro Cotellucci (Forschungszentrum Jülich)

07/11/2025, 17:20

Talk

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...

216. Renormalized quark masses using gradient flow

Oliver Witzel (Universität Siegen)

07/11/2025, 17:40

Talk

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...