Nucleon axial charge from quenched lattice QCD with domain wall fermions

TL;DR

This paper reports a lattice QCD calculation of the nucleon axial charge using domain wall fermions, highlighting finite volume effects and achieving results close to experimental values.

Contribution

It demonstrates the use of domain wall fermions and DBW2 gauge action to accurately compute nucleon axial charge with high statistics and finite volume analysis.

Findings

Finite volume effects significantly impact gA calculations.

Large volume lattice yields gA close to experimental value.

Chiral symmetry simplifies axial charge computation.

Abstract

We present a quenched lattice calculation of the nucleon isovector vector and axial-vector charges gV and gA. The chiral symmetry of domain wall fermions makes the calculation of the nucleon axial charge particularly easy since the Ward-Takahashi identity requires the vector and axial-vector currents to have the same renormalization, up to lattice spacing errors of order O(a^2). The DBW2 gauge action provides enhancement of the good chiral symmetry properties of domain wall fermions at larger lattice spacing than the conventional Wilson gauge action. Taking advantage of these methods and performing a high statistics simulation, we find a significant finite volume effect between the nucleon axial charges calculated on lattices with (1.2 fm)^3 and (2.4 fm)^3 volumes (with lattice spacing, a, of about 0.15 fm). On the large volume we find gA = 1.212 +/- 0.027(statistical error) +/- 0.024(normalization error). The quoted systematic error is the dominant (known) one, corresponding to current renormalization. We discuss other possible remaining sources of error. This theoretical first principles calculation, which does not yet include isospin breaking effects, yields a value of gA only a little bit below the experimental one, 1.2670 +/- 0.0030.