arXiv subjects

Agostino Patella

Publications and source records attributed to Agostino Patella.

At least 19 recordsLinked to original sources

arXiv2026

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. A central challenge is the renormalization of the energy-momentum tensor, which is complicated by the nonlinear realization of the $O(3)$ symmetry leading to non-trivial operator mixing patterns, and by large discretization artifacts affecting the determination of renormalization constants. We present results for the renormalization constants in the non-singlet sector, employing a modified lattice action with shifted boundary conditions and defining the renormalized coupling through the gradient flow. With this we obtain a precise determination of the renormalization constants $z_T$ and $Z_T$

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arXiv2026

Comparing RM123 and non-perturbative QCD+QED approaches to the HVP with 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 $g-2$. In recent work by the RC$^{\star}$ collaboration, 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 non-perturbative 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 $N_f =1+2+1$ 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. We summarize the comparison of the two approaches and discuss the implications for future lattice QCD+QED computations.

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arXiv2026

First-principle evaluation of inclusive hadronic $τ$ decays in QCD+QED

We present a strategy to extend lattice calculations of inclusive hadronic $τ$ decays from isosymmetric QCD to QCD+QED. The inclusive decay rate can be related to suitable Euclidean correlation functions, allowing for a first-principles evaluation of electromagnetic and isospin-breaking effects. Within the RM123 framework, radiative corrections are decomposed into leptonic, factorizable and non-factorizable contributions. We report preliminary results for the leptonic and factorizable terms in the electro-quenched approximation and discuss the remaining steps towards a complete calculation. This programme aims at a first-principles determination of inclusive $τ$ decay rates with direct implications for the extraction of the CKM matrix element $|V_{us}|$.

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arXiv2026

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.

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arXiv2025

Update on the isospin breaking corrections to the HVP with C-periodic boundary conditions

In the RC$^\star$ collaboration, we simulate lattice QCD+QED using $C-$periodic spatial boundary conditions to ensure that locality, gauge invariance, and translational invariance are preserved throughout the calculation. We present our progress in computing isospin-breaking (IB) corrections to the leading hadronic contribution to $(g-2)_μ$. We compare two ways of including the IB corrections: the RM123 method and dynamical QCD+QED simulations, both with $C-$periodic boundary conditions. The two calculations are performed at $β=3.24$ with four flavours of $\mathcal{O}(a)-$improved Wilson fermions; the QCD ensemble features $SU(3)-$symmetric sea quarks plus charm, while down and strange quarks are degenerate in QCD+QED gauge ensembles.

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arXiv2025

Error Scaling of Sea Quark Isospin-Breaking Effects

Sea-quark isospin-breaking effects (IBE) are difficult to compute since they require the evaluation of all-to-all propagators. However, the quest for high-precision calculations motivates a detailed study of these contributions. There are strong arguments that the stochastic error associated with these quantities should diverge in the continuum and infinite-volume limit, resulting in a possible bottleneck for the method. In this work, we present the study of the error scaling for these quantities using $N_f=3$ $O(a)$-improved Wilson fermions QCD with C-periodic boundary conditions in space, a pion mass $M_π=400$ MeV, a range of lattice spacings $a=0.05, 0.075, 0.1$ fm, and volumes $L=1.6, 2.4, 3.2$ fm. The analysis of the error as a function of the number of stochastic sources shows that we reach the gauge error for the dominant contributions. The errors do not show the leading order divergence $1/a$ for strong-IBE and $1/a^2$ for electromagnetic IBE, in the considered range of lattice spacings. On the other hand, our data are consistent with the predicted leading divergence $\sqrt{V}$.

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arXiv2025

Lattice gauge ensembles and data management

We summarize the status of lattice QCD ensemble generation efforts and their data management characteristics. Namely, these proceedings combine the contributions to a dedicated parallel session during the 41st International Symposium on Lattice Field Theory (Lattice 2024), during which representatives of 16 lattice QCD collaborations provided details on their simulation program, with focus on plans for publication, data management, and storage requirements. The parallel session was organized by the International Lattice Data Grid (ILDG), following an open call to the lattice QCD community for participation in the session.

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arXiv2025

Energy-momentum tensor in the 2d $O(3)$ non-linear sigma model on the lattice

The long-term goal of this project is the non-perturbative renormalization of the energy-momentum tensor in the 2d $O(3)$ non-linear sigma model using different methods which have been developed for QCD applications. As a first step, we have identified all operators that mix with the energy-momentum tensor once a lattice discretization is employed, that is all which are compatible with power counting and with the symmetries of the theory. Since these operators are constrained by non-linear Ward identities arising from the non-linear realization of the $O(3)$ symmetry, this is not entirely straightforward on the technical level. We have also outlined the basics of ongoing numerical simulations with shifted boundary conditions and an optimized constraint action to minimize lattice artifacts.

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arXiv2025

Partially connected contributions to baryon masses in QCD+QED

Full QCD+QED simulations allow to evaluate isospin breaking corrections to hadron masses. With the openQxD code, we are able to perform these simulations employing C-periodic boundary conditions, implemented through a doubling of the physical lattice along one spatial direction. The use of these boundary conditions introduces non-zero Wick contractions between two quark or two antiquark fields, that, in the case of the computation of baryon masses, lead to partially connected additional contributions that we expect to vanish in the infinite volume limit. These contributions are challenging because they involve an all-to-all propagator connecting one point in the physical lattice and one in the mirror lattice. We present a way to compute these corrections to the $Ω^-$ baryon mass using a combination of point and stochastic source inversions. This work is part of the program of the RC* collaboration.

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arXiv2025

$O(a)$-improved QCD+QED Wilson Dirac operator on GPUs

Markov Chain Monte Carlo simulations of lattice Quantum Chromodynamics (QCD) are the only known tool to investigate non-perturbatively the theory of the strong interaction and are required to perform precision tests of the Standard Model of Particle Physics. As the Markov Chain is a serial process, the sole option for improving the sampling rate is accelerating each individual update step. Heterogeneous clusters of GPU-accelerated nodes offer large total memory bandwidth which can be used to speed-up our application, openQxD-1.1, which is dominated by inversions of the Dirac operator, a large sparse matrix. In this work we investigate offloading the inversion to GPU using the lattice-QCD library QUDA, and our early results demonstrate a significant potential speed-up in the time-to-solution for state-of-the-art problem sizes. Minimal extensions to the existing QUDA library are required for our specific physics programme while greatly enhancing the performance portability of our code and retaining the reliability and robustness of existing applications in openQxD-1.1. Our new interface will enable us to utilize pre-exascale infrastructure and reduce the systematic uncertainty in our physics predictions by incorporating the effects of quantum electromagnetism (QED) in our simulations.

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arXiv2024

Scattering Amplitudes from Euclidean Correlators: Haag-Ruelle theory and approximation formulae

In this work we provide a non-perturbative solution to the theoretical problem of extracting scattering amplitudes from Euclidean correlators in infinite volume. We work within the solid axiomatic framework of the Haag-Ruelle scattering theory and derive formulae which can be used to approximate scattering amplitudes arbitrarily well in terms of linear combinations of Euclidean correlators at discrete time separations. Our result generalizes and extends the range of applicability of a result previously obtained by Barata and Fredenhagen [Commun. Math. Phys. 138 (1991) 507-520]. We provide a concrete procedure to construct such approximations, making our formulae ready to be used in numerical calculations of non-perturbative QCD scattering amplitudes. A detailed numerical investigation is needed to assess whether the proposed strategy can lead to the calculation of scattering amplitudes with phenomenologically satisfactory precision with presently available lattice QCD data. This will be the subject of future work. Nevertheless, the numerical accuracy and precision of lattice simulations is systematically improvable, and we have little doubts that our approach will become useful in the future.

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arXiv2024

An update on supersphere non linear sigma model on the lattice

We consider the discretized version of the sigma-model with supersphere target space $OSp(N+2m|2m)/OSp(N+2m-1|2m)$ and present a preliminary numerical study of bosonic and fermionic two-point functions for the cases $OSp(3|2)$ and $OSp(5|2)$. We observe consistency with the expectations of this supersymmetric setup and discuss the sign problem.

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arXiv2023

Hutch++ and XTrace to Improve Stochastic Trace Estimation

We present the analysis of two recently proposed noise reduction techniques, Hutch++ and XTrace, both based on inexact deflation. These methods were proven to have a better asymptotic convergence to the solution than the classical Girard-Hutchinson stochastic method. We applied these methods to the computation of the trace of the inverse of the Dirac operator with $O(a)$ improved Wilson fermions on the QCD ensemble generated by the RC$^{\star}$ collaboration with $m_π\approx 400$ MeV and $V = 64\times 32^3$. Unfortunately, we see no noise reduction with a moderate number of sources, and we attempt an explanation of why this is the case. This study was part of the effort to evaluate isospin-breaking effects using the RM123 with C$^{\star}$ boundary conditions in an unquenched set-up.

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arXiv2023

Tuning of QCD+QED simulations with C$^{\star}$ boundary conditions

We give an update on the ongoing effort of the RC$^\star$ collaboration to generate fully dynamical QCD+QED ensembles with C$^\star$ boundary conditions using the openQ$^\star$D code. The simulations were tuned to the U-symmetric point ($m_d = m_s$) with pions at $m_{π^{\pm}} \approx 400$ MeV. The splitting of the light mesons is used as one of three tuning observables and fixed to $m_{K^{0}} - m_{K^{\pm}} \approx 5$ MeV and $m_{K^{0}} - m_{K^{\pm}} \approx 25$ MeV on ensembles with renormalized electromagnetic coupling $α_{\text{R}} \approx α_{\text{phys}}$ and $α_R \approx 5.5α_{phys}$ respectively. The tuning of the three independent quark masses to the desired lines of constant physics is particularly challenging. We will define the chosen hadronic renormalization scheme, and we will present a tuning strategy based on a combination of mass reweighting and linear interpolation to explore the parameter space. We will comment on finite-volume effects comparing meson masses on two different volumes with $m_{π^{\pm}} L \approx 3.2$ and $m_{π^{\pm}} L \approx 5.1$. We will also provide some technical details on our updated strategy to calculate the sign of the fermionic Pfaffian, which arises in presence of C$^\star$ boundary conditions in place of the standard fermionic determinant. More technical details on the generation of the configurations can be found in J. Lücke's proceedings

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arXiv2023

$N_f = 1+2+1$ QCD+QED simulations with C$^\star$ boundary conditions

We give an update on the ongoing effort of the RC$^\star$ collaboration to generate fully dynamical QCD+QED configurations with C$^\star$ boundary conditions using the openQ$^\star$D code. The simulations are tuned to the U-symmetric point ($m_d=m_s$) with pions at $m_{π^\pm}\approx 400$ MeV. The splitting of the light mesons is used as one of three tuning observables and fixed to $m_{K^0} - m_{K^\pm} \approx 5$ MeV and $m_{K^0} - m_{K^\pm} \approx 25$ MeV on ensembles with renormalized electromagnetic coupling $α_\mathrm{R} \approx α_\mathrm{phys.}$ and $α_\mathrm{R}\approx 5.5 α_\mathrm{phys.}$ respectively. We will discuss some details concerning our tuning strategy and present the calculation of the meson and baryon masses. Finally, we will also present a cost analysis for our simulations. More technical details on finite-volume effects and the tuning can be found in A. Cotellucci's proceedings.

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arXiv2023

Strange and charm contributions to the HVP from C* boundary conditions

We present preliminary results for the determination of the leading strange and charm quark-connected contributions to the hadronic vacuum polarization contribution to the muon's g-2. Measurements are performed on the RC* collaboration's QCD ensembles, with 3+1 flavors of O(a) improved Wilson fermions and C* boundary conditions. The HVP is computed on a single value of the lattice spacing and two lattice volumes at unphysical pion mass. In addition, we compare the signal-to-noise ratio for different lattice discretizations of the vector current.

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arXiv2022

Hadronic vacuum polarization with C* boundary conditions

We present a progress report on the calculation of the connected hadronic contribution to the muon g-2 with C* boundary conditions. For that purpose we use a QCD gauge ensemble with 3+1 flavors and two QCD+QED gauge ensembles with 1+2+1 flavors of dynamical quarks generated by the RC* collaboration. We detail the calculation of the vector mass and elaborate on both statistical and systematic errors.

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arXiv2022

Supersphere non-linear sigma model on the lattice

Two-dimensional $O(N)$ non-linear sigma models are exactly solvable theories and have many applications, from statistical mechanics to their use as QCD toy models. We consider a supersymmetric extension, the non-linear sigma model on the supersphere~$S^{N+2m-1|2m}\equiv \frac{OSP(N+2m|2m)}{OSP(N+2m-1|2m)}$. We briefly describe its renormalization properties and lattice discretization, and present a strategy for numerical simulations together with some preliminary numerical results.

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