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

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_π= 250 MeV pion mass, corresponding to the finite-size scaling parameter m_πL \sim 5.8, agrees well with an earlier result at a^{-1}=1.7 GeV, L = 2.8 fm, and m_π= 420 MeV, with similar m_πL. 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_πL. We also report the result from the lighter, m_π= 170 MeV ensemble.

7 pages, 5 figures, talk presented at Lattice 2012, Cairns, QLD, June 24-29, 2012