Quark mass dependence of the nucleon axial-vector coupling constant

TL;DR

This paper investigates how the nucleon axial-vector coupling constant g_A depends on quark mass, comparing chiral effective field theory models with and without explicit Delta resonance, to improve lattice QCD extrapolations to physical pion mass.

Contribution

It demonstrates that including the Delta(1230) resonance explicitly is essential for accurate chiral extrapolation of g_A from lattice QCD data.

Findings

Including Delta resonance improves extrapolation accuracy.

The extrapolation function aligns well with lattice data.

Long- and short-distance physics interplay enhances the model.

Abstract

We study the quark mass expansion of the axial-vector coupling constant g_A of the nucleon. The aim is to explore the feasibility of chiral effective field theory methods for extrapolation of lattice QCD results - so far determined at relatively large quark masses corresponding to pion masses larger than 0.6 GeV - down to the physical value of the pion mass. We compare two versions of non-relativistic chiral effective field theory: One scheme restricted to pion and nucleon degrees of freedom only, and an alternative approach which incorporates explicit Delta(1230) resonance degrees of freedom. It turns out that, in order to approach the physical value of g_A in a leading-one-loop calculation, the inclusion of the explicit Delta(1230) degrees of freedom is crucial. With information on important higher order couplings constrained from analyses of inelastic pion production processes, a chiral extrapolation function for g_A is obtained, which works well from the chiral limit across the physical point into the region of present lattice data. The resulting enhancement of our extrapolation function near the physical pion mass is found to arise from an interplay between long- and short- distance physics.