Nucleon axial form factor from lattice QCD

Results for the isovector axial form factors of the proton from a lattice QCD calculation are presented for both the point-split and local currents. They are obtained on a quenched ${16}^3$ × 24 lattice at $\beta =6.0\mathrm{}$ with Wilson fermions for a range of quark masses from strange to twice the charm mass. For each quark mass, we find that the axial form factor falls off slower than the corresponding proton electric form factor. Results extrapolated to the chiral limit show that the $q^2$ dependence of the axial form factor agrees quite well with experiment. The axial vector coupling constant $g_A$ calculated for the point-split and local currents is 1.20 ± 0.11 and 1.18 ± 0.11. The central values are 4% and 6% smaller than the experimental value of 1.254, respectively. We also consider the large $\mathrm{ma}$ correction and renormalization for the axial vector current of heavy quarks.