Dressed-quarks and the nucleon's axial charge

TL;DR

This paper investigates how dynamical chiral symmetry breaking influences the nucleon's axial charge and reveals that nonperturbative effects are essential for aligning theoretical predictions with experimental data.

Contribution

It demonstrates the impact of dynamical chiral symmetry breaking on the nucleon's axial charge and highlights the importance of nonperturbative effects in theoretical models.

Findings

g_A^q is suppressed at infrared momenta due to DCSB

Inclusion of nonperturbative effects inflates g_A^q value

Agreement with experimental g_A requires improved Faddeev kernel

Abstract

The nucleon's axial charge, g_A, expresses features that are both fundamental to the strong interaction and crucial to its connection with weak interaction physics. We show that dynamical chiral symmetry breaking (DCSB) suppresses the axial-charge of a dressed-quark, g_A^q, at infrared momenta. Since this effect disappears as chiral symmetry is restored, one may argue that g_A vanishes with the restoration of chiral symmetry because no nucleon bound-state survives the associated transition. The suppression of g_A^q is shown to be part of an explanation for a 25% reduction of g_A from its nonrelativistic quark-model value. Critical too, however, is the presence of dressed-quark angular momentum within the nucleon. The value of g_A^q depends on the kernels of the gap and Bethe-Salpeter equations. We find that incorporation of essentially nonperturbative effects associated with DCSB into these kernels inflates the value relative to that obtained at leading-order in a widely used truncation of QCD's Dyson-Schwinger equations. Such corrections also affect the nucleon's axial radius. In both cases, however, agreement with experiment will require similar improvements to the Faddeev kernel and associated interaction current.