Power Counting Regime of Chiral Extrapolation and Beyond

TL;DR

This paper uses finite-range regularised chiral effective field theory to estimate the power-counting regime of chiral perturbation theory, finding it valid only for pion masses below 180 MeV, slightly above the physical mass.

Contribution

It introduces a method to estimate the power-counting regime of chiral perturbation theory using FRR techniques, extending understanding of its applicability in lattice QCD.

Findings

PCR extends only slightly beyond physical pion mass

PCR limit is approximately 180 MeV for 1% tolerance

Provides a quantitative estimate of chiral expansion validity

Abstract

Finite-range regularised (FRR) chiral effective field theory is presented in the context of approximation schemes ubiquitous in modern lattice QCD calculations. Using FRR techniques, the power-counting regime (PCR) of chiral perturbation theory can be estimated. To fourth-order in the expansion at the 1% tolerance level, we find m_\pi < 180 MeV for the PCR, extending only a small distance beyond the physical pion mass.