Sea-quark effects in nucleon structure

We report results of our calculation on the π N σ term and the flavor-singlet axial charge of the nucleon in the framework of quenched lattice QCD. The disconnected insertions which involve contributions from the sea quarks are evaluated with the stochastic estimator with the Z₂ noise which yields minimum variances. We find the sea-quark contribution to the πN sigma term to be∼ 1 2 - 1 4 of that of the dynamical fermion calculation. Whereas, the sea-quark contribution to the flavor-singlet g_A is negative and large enough to cancel the valence (connected insertion) contribution substantially to resolve the "proton spin crisis".