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

TL;DR

This paper presents a lattice QCD calculation of isospin-breaking corrections to the muon magnetic anomaly, providing the most precise estimate to date for these effects on the hadronic vacuum polarization contribution.

Contribution

The study introduces a detailed lattice QCD approach to quantify electromagnetic and strong isospin-breaking effects on the muon g-2, improving accuracy over previous estimates.

Findings

Isospin-breaking correction for light quarks: 7.1(2.5) x 10^{-10}

Strange quark correction: -0.0053(33) x 10^{-10}

Charm quark correction: 0.0182(36) x 10^{-10}

Abstract

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 $\delta a_\mu^{\rm HVP}(ud) = 7.1 ~ (2.5) \cdot 10^{-10}$, $\delta a_\mu^{\rm HVP}(s) = -0.0053 ~ (33) \cdot 10^{-10}$ and $\delta a_\mu^{\rm HVP}(c) = 0.0182 ~ (36) \cdot 10^{-10}$. At leading order in $\alpha_{em}$ and $(m_d - m_u) / \Lambda_{QCD}$ we obtain $\delta a_\mu^{\rm HVP}(udsc) = 7.1 ~ (2.9) \cdot 10^{-10}$, which is currently the most accurate determination of the IB corrections to $a_\mu^{\rm HVP}$.