Mixed Action Lattice Spacing Effects on the Nucleon Axial Charge

We study the nucleon axial charge in the chiral perturbation theory for a mixed lattice action of Ginsparg-Wilson valence quarks and staggered sea quarks. In particular, we investigate the lattice spacing $a^2$-dependence of the neutron to proton axial transition matrix element. By using the known low-energy constants (LEC's) and an estimated value of a new LEC which appears in the calculation, we see a large lattice spacing effect on $g_A$.