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 16(3) x 32 and 24(3) x 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(pi) is 7360 units, including 900 for thermalization. We find finite volume effects are larger than the pion mass dependence at m(pi) = 330 MeV. We also find a scaling with the single variable m(pi)L 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(pi)=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.