Pion-Nucleon Sigma Term with Dynamical Wilson Fermions

We calculate connected and disconnected contributions to the flavor singlet scalar density amplitude of the nucleon in a full QCD lattice simulation with n(f) = 2 dynamical Wilson fermions at beta = 5.6 on a 16(3) x 32 lattice. We find that both contributions are of similar size at the light quark mass. We arrive at the estimate sigma(pi N) = 18(5) MeV. Its smallness is directly related to the apparent decrease of u, d quark masses when unquenching QCD lattice simulations. The y parameter can be estimated from a semi-quenched analysis, in which there are no strange quarks in the sea, the result being y = 0.59(13). [S0556-2821(99)02205-5].