Pion-nucleon sigma term in lattice QCD.

Abstract

We calculate both connected and disconnected contribution to the $\pi$-$N$ $\sigma$-term in quenched lattice QCD with Wilson quark action on a $12^3\times 20$ lattice at $\beta=5.7$. The latter is evaluated with the aid of the variant wall source method, which was previously applied successfully for extraction of $\pi$-$\pi$ scattering lengths and $\eta^\prime$ meson mass. We found that the disconnected contribution is about twice larger than the connected one. The value for the full $\pi$-$N$ $\sigma$ term $\sigma=40-60$ MeV is consistent with the experimental estimates. The nucleon matrix element of the strange quark density $\bar s s$ is fairly large in our result.