Lattice Calculation of Nucleon Isovector Axial Charge with Improved Currents

TL;DR

This study improves the calculation of the nucleon isovector axial charge using dimension-4 operators and overlap fermions, achieving results closer to experimental values by reducing systematic errors and accounting for excited-state contamination.

Contribution

The paper introduces an improved current operator method with dimension-4 operators in lattice QCD to more accurately compute nucleon axial charge, demonstrating enhanced agreement with experimental data.

Findings

Improved axial charge values are increased by a few percent towards experimental results.

The method reduces excited-state contamination effects in the calculation.

Consistent results are obtained using both overlap and clover fermions on the same configurations.

Abstract

We employ dimension-4 operators to improve the local vector and axial-vector currents and calculate the nucleon isovector axial coupling $g^3_A$ with overlap valence on $2+1$-flavor Domain Wall Fermion sea. Using the equality of $g^3_A$ 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 $g_A^{3}(24I)=1.22(4)$ and $g_A^{3}(32I)=1.21(3)$ are obtained on a $24^3\times 64$ lattice at pion mass of 330 MeV and a $32^3\times 64$ lattice at pion mass 300 MeV are increased by $3.4\%$ and $1.7\%$ from their unimproved values, respectively. We have also used clover fermion on the same DWF configurations and find the same behavior for the local axial charge as that of the overlap fermion.