Nucleon Axial Charge in (2+1)-Flavor Dynamical-Lattice QCD with Domain-Wall Fermions

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 16³×32 and 24³×64 lattices (L=1.8 and 2.7 fm) with length 16 in the fifth dimension. The length of the Monte Carlo trajectory at the lightest m_π is 7360 units, including 900 for thermalization. We find finite volume effects are larger than the pion mass dependence at m_π=330  MeV. We also find a scaling with the single variable m_πL which can also be seen in previous two-flavor domain wall and Wilson fermion calculations. Using this scaling to eliminate the finite-volume effect, we obtain g_A=1.20(6)(4) at the physical pion mass, m_π=135  MeV, where the first and second errors are statistical and systematic. The observed finite-volume scaling also appears in similar quenched simulations, but disappear when V≥(2.4  fm)³. We argue this is a dynamical quark effect.