Structure-Dependent Electromagnetic Finite-Size Effects

TL;DR

This paper develops a model-independent, relativistic method to analytically calculate electromagnetic finite-size effects in particles, crucial for precision tests in flavor physics from lattice simulations.

Contribution

It introduces a novel approach using electromagnetic Ward identities to derive finite-size effects, incorporating structure via physical form-factors, applicable to pseudoscalar masses and decay amplitudes.

Findings

Derived finite-size effects for pseudoscalar mass at order 1/L^3

Calculated finite-size effects in leptonic decay amplitudes at order 1/L^2

Method enhances precision in Standard Model tests from lattice QCD simulations

Abstract

We present a model-independent and relativistic approach to analytically derive electromagnetic finite-size effects beyond the point-like approximation. The key element is the use of electromagnetic Ward identities to constrain vertex functions, and structure-dependence appears via physical form-factors and their derivatives. We apply our general method to study the leading finite-size structure-dependence in the pseudoscalar mass (at order $1/L^3$) as well as in the leptonic decay amplitudes of pions and kaons (at order $1/L^2$). Knowledge of the latter is essential for Standard Model precision tests in the flavour physics sector from lattice simulations.