Flavor-SingletgAfrom Lattice QCD

Abstract

We report on a lattice QCD calculation of the flavor-singlet axial coupling constant g_A of the proton from the axial-vector current. The simulation is carried out at \beta = 6 on a quenched 16^3 \times 24 lattice. An extrapolation to the chiral limit shows that the connected insertion (valence and cloud parts) is 0.62 \pm 0.09, which is close to g_A^8. The disconnected insertion (vacuum polarization from the sea quark) for the u or d quark is - 0.12\pm 0.01 and the s quark also contributes -0.12\pm 0.01. The total g_A^1 is thus 0.25 \pm 0.12 which is in agreement with experiments. In addition, we find g_A^3 = 1.20 \pm 0.11, g_A^8 = 0.61 \pm 0.13 and F_A/D_A = 0.60 \pm 0.02, also in agreement with experiments