Lattice calculation of nucleon isovector axial charge with improved currents

Abstract

We employ dimension-4 operators to improve the local vector and axial-vector currents and calculate the nucleon isovector axial coupling ${g}_{A}^{3}$ with overlap valence on $2+1$-flavor domain wall fermion (DWF) sea. Using the equality of ${g}_{A}^{3}$ from the spatial and temporal components of the axial-vector current as a normalization condition, we find that ${g}_{A}^{3}$ is increased by a few percent towards the experimental value. The excited-state contamination has been taken into account with three time separations between the source and sink. The improved axial charges ${g}_{A}^{3}(24I)=1.22(4)(3)$ and ${g}_{A}^{3}(32I)=1.21(3)(3)$ are obtained on a $2{4}^{3}\ifmmode\times\else\texttimes\fi{}64$ lattice at pion mass of 330 MeV and a $3{2}^{3}\ifmmode\times\else\texttimes\fi{}64$ lattice at pion mass 300 MeV and are increased by 3.4% and 1.7% from their unimproved values, respectively. We have also used clover fermions on the same DWF configurations and find the same behavior for the local axial charge as that with overlap fermions.