Nucleon axial charge in 2+1-flavor dynamical DWF lattice QCD

Abstract

The current status of some nucleon isovector observables, the vector charge, \(g_V\), axial charge, \(g_A\), quark momentum fraction, \(\langle x \rangle_{u-d}\), and quark helicity fraction, \(\langle x \rangle_{\Delta u - \Delta d}\), calculated using recent RBC/UKQCD 2+1-flavor dynamical domain-wall fermions (DWF) lattice QCD ensembles are reported: with Iwasaki gauge action at inverse lattice spacing, \(a^{-1}\), of about 1.7 GeV, linear lattice extent, \(L\), of about 2.7 fm, pion mass, \(m_\pi\), of about 420 and 330 MeV, and with Iwasaki\(\times\)DSDR gauge action at \(a^{-1}\) of about 1.4 GeV, \(L\) of about 4.6 fm, and \(m_\pi\) of about 250 and 170 MeV. The calculations have been refined with enhanced statistics, in particular through successful application of the all-mode-averaging (AMA) technique for the 170- and 330-MeV ensembles. As a result, the precision agreement seen in the charge ratio, \(g_A/g_V\), for 420-MeV and 250-MeV ensembles that share the finite-size scaling parameter \(m_\pi L\) of about 5.8 is more significant with new values of 1.17(2) and 1.18(4) respectively. We also studied the dependence on the source-sink separation in the lightest ensemble of 170-MeV, by comparing the cases with the separation of about 1.0 and 1.3 fm and did not see any dependence: contamination from the excited states are well under control in our choice of source and sink smearing. The axial charge, \(g_A\) and the ratio, \(g_A/g_V\), shows a long-range autocorrelation that extends the entire range of configurations that were so far analyzed, almost 700 hybrid Molecular Dynamics time, in the lightest ensemble of \(m_\pi=170\) MeV. The other observables do not show any autocorrelation with the interval of 16 trajectories.

Comments: 7 pages, 12 figures, a talk presented at the 31st International Symposium on Lattice Field Theory, LATTICE 2013, July 29 - August 3, 2013, Mainz, Germany