Flavor-singlet gA from lattice QCD

We report on a lattice QCD calculation of the flavor-singlet axial coupling constant gA of the proton from the axial-vector current. The simulation is carried out at =6 on a quenched 163×24 lattice. An extrapolation to the chiral limit shows that the connected insertion (valence and cloud parts) is 0.620.09, which is close to gA8. The disconnected insertion (vacuum polarization from the sea quark) for the u or d quark is -0.120.01 and the s quark also contributes -0.120.01. The total gA0 is thus 0.250.12, which is in agreement with experiments. In addition, we find gA3=1.200.11, gA8=0.610.13, and FA/DA=0.600.02, also in agreement with experiments.