Finite-size scaling in nucleon axial charge from 2+1-flavor DWF lattice QCD

TL;DR

This paper discusses ongoing lattice-QCD calculations of the nucleon axial charge, highlighting finite-size effects and systematic errors, with results from different ensembles indicating a finite-size scaling behavior.

Contribution

It provides new insights into finite-size effects on nucleon axial charge calculations using 2+1-flavor DWF lattice QCD at different pion masses and volumes.

Findings

Finite-size effects likely cause a 10% deficit in g_A.

Results are consistent across ensembles with similar m_L.

Excited-state contamination appears to be a small systematic error.

Abstract

We report the current status of the on-going lattice-QCD calculations of nucleon isovector axial charge, g_A, using the RBC/UKQCD 2+1-flavor dynamical domain-wall fermion ensembles at lattice cutoff of about a^{-1}=1.4 GeV in a spatial volume (L = 4.6 fm)^3. The result from the ensemble with m_\pi = 250 MeV pion mass, corresponding to the finite-size scaling parameter m_\pi L \sim 5.8, agrees well with an earlier result at a^{-1}=1.7 GeV, L = 2.8 fm, and m_\pi = 420 MeV, with similar m_\pi L. This suggests the systematic error from excited-state contamination is small in both ensembles and about 10-% deficit in g_A we are observing is likely a finite-size effect that scales with m_\pi L. We also report the result from the lighter, m_\pi = 170 MeV ensemble.