arXiv subjects

Davide Giusti

Publications and source records attributed to Davide Giusti.

13 recordsLinked to original sources

arXiv2026

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

We present an update on 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$_{\text{L}}$. We give an update on the isosymmetric value and the current determination used to compute the gradient-flow scale $w_{0}$, then we present some preliminary results of the valence-valence contribution to the axial-pseudoscalar correlator for different volumes and lattice spacings. We also discuss the next steps and plans.

hep-lat↗

arXiv2026

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 hybrid determination of the hadronic vacuum polarisation contribution to a precision of 0.45%

hep-lat↗

arXiv2025

Efficient lattice QCD computation of radiative-leptonic-decay form factors at multiple positive and negative photon virtualities

In previous work Phys. Rev. D 107, 074507 (2023), we showed that form factors for radiative leptonic decays of pseudoscalar mesons can be determined efficiently and with high precision from lattice QCD using the ``3d method,'' in which three-point functions are computed for all values of the current-insertion time and the time integral is performed at the data-analysis stage. Here, we demonstrate another benefit of the 3d method: the form factors can be extracted for any number of nonzero photon virtualites from the same three-point functions at no extra cost. We present results for the $D_s\to\ell\nu\gamma^*$ vector form factor as a function of photon energy and photon virtuality, for both positive and negative virtuality. In our analysis, we separately consider the two different time orderings and the different quark flavors in the electromagnetic current. We discuss in detail the behavior of the unwanted exponentials contributing to the three-point functions, as well as the choice of fit models and fit ranges used to remove them for various values of the virtuality. While positive photon virtuality is relevant for decays to multiple charged leptons, negative photon virtuality suppresses soft contributions and is of interest in QCD-factorization studies of the form factors.

hep-lat↗

arXiv2025

Kaon Physics: A Cornerstone for Future Discoveries

The kaon physics programme, long heralded as a cutting-edge frontier by the European Strategy for Particle Physics, continues to stand at the intersection of discovery and innovation in high-energy physics (HEP). With its unparalleled capacity to explore new physics at the multi-TeV scale, kaon research is poised to unveil phenomena that could reshape our understanding of the Universe. This document highlights the compelling physics case, with emphasis on exciting new opportunities for advancing kaon physics not only in Europe but also on a global stage. As an important player in the future of HEP, the kaon programme promises to drive transformative breakthroughs, inviting exploration at the forefront of scientific discovery.

hep-ph↗

arXiv2023

Methods for high-precision determinations of radiative-leptonic decay form factors using lattice QCD

We present a study of lattice-QCD methods to determine the relevant hadronic form factors for radiative leptonic decays of pseudoscalar mesons. We provide numerical results for $D_s^+ \to \ell^+ νγ$. Our calculation is performed using a domain-wall action for all quark flavors and on a single RBC/UKQCD lattice gauge-field ensemble. The first part of the study is how to best control two sources of systematic error inherent in the calculation, specifically the unwanted excited states created by the meson interpolating field, and unwanted exponentials in the sum over intermediate states. Using a 3d sequential propagator allows for better control over unwanted exponentials from intermediate states, while using a 4d sequential propagator allows for better control over excited states. We perform individual analyses of the 3d and 4d methods as well as a combined analysis using both methods, and find that the 3d sequential propagator offers good control over both sources of systematic uncertainties for the smallest number of propagator solves. From there, we further improve the use of a 3d sequential propagator by employing an infinite-volume approximation method, which allows us to calculate the relevant form factors over the entire allowed range of photon energies. We then study improvements gained by performing the calculation using a different three-point function, using ratios of three-point functions, averaging over positive and negative photon momentum, and using an improved method for extracting the structure-dependent part of the axial form factor. The optimal combination of methods yields results for the $D_s^+ \to \ell^+ νγ$ structure-dependent vector and axial form factors in the entire kinematic range with statistical plus fitting uncertainties of order 5%, using 25 gauge configurations with 64 samples per configuration.

hep-lat↗

arXiv2022

A lattice QCD perspective on weak decays of b and c quarks Snowmass 2022 White Paper

Lattice quantum chromodynamics has proven to be an indispensable method to determine nonperturbative strong contributions to weak decay processes. In this white paper for the Snowmass community planning process we highlight achievements and future avenues of research for lattice calculations of weak $b$ and $c$ quark decays, and point out how these calculations will help to address the anomalies currently in the spotlight of the particle physics community. With future increases in computational resources and algorithmic improvements, percent level (and below) lattice determinations will play a central role in constraining the standard model or identifying new physics.

hep-lat↗

arXiv2021

Controlling unwanted exponentials in lattice calculations of radiative leptonic decays

Two important sources of systematic errors in lattice QCD calculations of radiative leptonic decays are unwanted exponentials in the sum over intermediate states and unwanted excited states created by the meson interpolating field. Performing the calculation using a 3d sequential propagator allows for better control over the systematic uncertainties from intermediate states, while using a 4d sequential propagator allows for better control over the systematic uncertainties from excited states. We calculate form factors using both methods and compare how reliably each controls these systematic errors. We also employ a hybrid approach involving global fits to data from both methods.

hep-lat↗

arXiv2021

Window contributions to the muon hadronic vacuum polarization with twisted-mass fermions

We present a lattice calculation of the Euclidean position-space windows contributing to the leading-order hadronic vacuum polarization term of the muon anomalous magnetic moment $a_μ$. Short-, intermediate- and long-distance windows are considered in order to isolate different scales sensitive to specific integration ranges of experimental time-like data used in the R-ratio. By adopting the same smooth window function introduced by the RBC and UKQCD Collaborations with width parameter $Δ= 0.15~\rm fm$, for the isospin-symmetric, light, quark-connected component we get $a_μ^{\rm SD} (ud) = 48.21\,(80) \cdot 10^{-10}$ , $a_μ^{\rm W} (ud) = 202.2\,(2.6) \cdot 10^{-10}$ and $a_μ^{\rm LD} (ud) = 382.5\,(11.7) \cdot 10^{-10}$ in the short- (SD), intermediate- (W) and long-distance (LD) time regions, respectively, with $t_0 = 0.4~\rm fm$ and $t_1 = 1.0~\rm fm$. Our results are obtained using the gauge configurations generated by the Extended Twisted Mass Collaboration with $N_f=2+1+1$ dynamical quarks, at three values of the lattice spacing varying from 0.089 to 0.062 fm, at several lattice volumes and with pion masses in the range $M_π\simeq 220 - 490~\rm MeV$.

hep-lat↗

arXiv2021

A new framework to tune an improved relativistic heavy-quark action

We introduce a new non-perturbative method to tune the parameters of the Columbia formulation of an anisotropic, clover-improved relativistic heavy-quark (RHQ) action. By making use of suitable observables which can be computed at a sequence of heavy-quark mass values, employing an $O(a)$-improved discretized action with domain-wall chiral fermion, and safely interpolated between the accessible heavy-quark mass region and the static point predicted by heavy-quark effective theory, we are able to precisely determine the unknown coefficients of the RHQ action. In this proof-of-principle study we benefit from the RBC/UKQCD Iwasaki gauge configurations with $2+1$ flavors of dynamical quarks, at three values of the lattice spacing varying from $0.11$ to $0.062$ fm. Preliminary results and applications to bottom spectroscopy are also presented.

hep-lat↗

arXiv2019

The hadronic vacuum polarization contribution to $(g_μ-2)$: Lattice QCD+QED calculations

The anomalous magnetic moment of the muon $a_μ$ is one of the most accurate quantities in Particle Physics. The long-standing discrepancy of about $3.7$ standard deviations between the experimental value and the prediction of the Standard Model could represent an intriguing indication of New Physics. The experiments at Fermilab (E989) and at J-PARC (E34) aim at reducing significantly the experimental uncertainty, thus making the theoretical one due to hadronic corrections the main limitation of this stringent test of the Standard Model. In this contribution we present the results of a first-principles lattice calculation of the hadronic vacuum polarization (HVP) contribution to $a_μ$, including electromagnetic and $SU(2)$-breaking corrections. Our determination, $a_μ^{\rm HVP} = 682.0 ~ (18.7) \cdot 10^{-10}$, turns out to be in agreement with recent theoretical determinations based on the dispersive analyses of the experimental cross section data for the annihilation process $e^+e^- \to hadrons$. Furthermore, we provide for the first time a lattice estimate for the missing part of $a_μ^{\rm HVP}$ not covered in the MUonE experiment, $\left[a_μ^{\rm HVP}\right]_> = 91.6 ~ (2.0) \cdot 10^{-10}$.

hep-lat↗

arXiv2019

Isospin-breaking corrections to the muon magnetic anomaly in Lattice QCD

In this contribution we present a lattice calculation of the leading-order electromagnetic and strong isospin-breaking (IB) corrections to the quark-connected hadronic-vacuum-polarization (HVP) contribution to the anomalous magnetic moment of the muon. The results are obtained adopting the RM123 approach in the quenched-QED approximation and using the QCD gauge configurations generated by the ETM Collaboration with $N_f = 2+1+1$ dynamical quarks, at three values of the lattice spacing ($a \simeq 0.062, 0.082, 0.089$ fm), at several lattice volumes and with pion masses between $\simeq 210$ and $\simeq 450$ MeV. After the extrapolations to the physical pion mass and to the continuum and infinite-volume limits the contributions of the light, strange and charm quarks are respectively equal to $δa_μ^{\rm HVP}(ud) = 7.1 ~ (2.5) \cdot 10^{-10}$, $δa_μ^{\rm HVP}(s) = -0.0053 ~ (33) \cdot 10^{-10}$ and $δa_μ^{\rm HVP}(c) = 0.0182 ~ (36) \cdot 10^{-10}$. At leading order in $α_{em}$ and $(m_d - m_u) / Λ_{QCD}$ we obtain $δa_μ^{\rm HVP}(udsc) = 7.1 ~ (2.9) \cdot 10^{-10}$, which is currently the most accurate determination of the IB corrections to $a_μ^{\rm HVP}$.

hep-lat↗

arXiv2018

Radiative corrections to decay amplitudes in lattice QCD

The precision of lattice QCD computations of many quantities has reached such a precision that isospin-breaking corrections, including electromagnetism, must be included if further progress is to be made in extracting fundamental information, such as the values of Cabibbo-Kobayashi-Maskawa matrix elements, from experimental measurements. We discuss the framework for including radiative corrections in leptonic and semileptonic decays of hadrons, including the treatment of infrared divergences. We briefly review isospin breaking in leptonic decays and present the first numerical results for the ratio $Γ(K_{\mu2})/Γ(π_{\mu2})$ in which these corrections have been included. We also discuss the additional theoretical issues which arise when including electromagnetic corrections to semileptonic decays, such as $K_{\ell3}$ decays. The separate definition of strong isospin-breaking effects and those due to electromagnetism requires a convention. We define and advocate conventions based on hadronic schemes, in which a chosen set of hadronic quantities, hadronic masses for example, are set equal in QCD and in QCD+QED. This is in contrast with schemes which have been largely used to date, in which the renormalised $α_s(μ)$ and quark masses are set equal in QCD and in QCD+QED in some renormalisation scheme and at some scale $μ$.

hep-lat↗

arXiv2018

HVP contribution of the light quarks to the muon $(g - 2)$ including isospin-breaking corrections with Twisted-Mass fermions

We present a preliminary lattice calculation of the leading-order electromagnetic and strong isospin-breaking corrections to the Hadronic Vacuum Polarization (HVP) contribution of the light quarks to the anomalous magnetic moment of the muon. The results are obtained in the quenched-$QED$ approximation using the $QCD$ gauge configurations generated by the European Twisted Mass Collaboration (ETMC) with $N_f = 2 + 1 + 1$ dynamical quarks, at three values of the lattice spacing varying from $0.089$ to $0.062 ~ \mbox{fm}$, at several lattice volumes and with pion masses in the range $M_π\simeq 220 ÷490 ~ \mbox{MeV}$.

hep-lat↗