Electromagnetic pion mass splitting using PV-regulated photon propagator

TL;DR

This paper introduces a continuum, infinite-volume approach using PV-regulated photon propagator to accurately compute electromagnetic effects, demonstrated on the pion mass difference with lattice QCD.

Contribution

It presents a novel PV-regulated photon propagator method for electromagnetic corrections, avoiding finite-volume effects and enabling precise phenomenological comparisons.

Findings

Successful application to pion mass splitting

Reduction of finite-volume effects in electromagnetic calculations

Potential for improved accuracy in hadronic observable predictions

Abstract

Several hadronic observables are nowadays computed in lattice QCD with a sub-percent precision which requires the inclusion of strong 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 and do not allow for a straightforward crosscheck against phenomenology and other calculations. Both issues can be avoided by working with a Pauli-Villars regulated photon propagator defined directly in the continuum and infinite volume. This methodology can be profitably exploited to improve the determination of leading-order electromagnetic corrections to several observables such as the HVP or nucleon masses. In this work we apply the strategy to the charged/neutral pion mass difference using CLS ensembles.