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تسجيل مستخدم جديدFinite-size scaling in nucleon axial charge from 2+1-flavor DWF lattice QCD
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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.
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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.
We present results for the nucleon axial charge g_A at a fixed lattice spacing of 1/a=1.73(3) GeV using 2+1 flavors of domain wall fermions on size 16^3x32 and 24^3x64lattices (L=1.8 and 2.7 fm) with length 16 in the fifth dimension. The length of th
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