Nucleon mass, sigma term and lattice QCD

We investigate the quark mass dependence of the nucleon mass M_N. An interpolation of this observable, between a selected set of fully dynamical two-flavor lattice QCD data and its physical value, is studied using relativistic baryon chiral perturbation theory up to order p^4. In order to minimize uncertainties due to lattice discretization and finite volume effects our numerical analysis takes into account only simulations performed with lattice spacings a<0.15 fm and m_pi L>5. We have also restricted ourselves to data with m_pi<600 MeV and m_sea=m_val. A good interpolation function is found already at one-loop level and chiral order p^3. We show that the next-to-leading one-loop corrections are small. From the p^4 numerical analysis we deduce the nucleon mass in the chiral limit, M_0 approx 0.88 GeV, and the pion-nucleon sigma term sigma_N= (49 +/- 3) MeV at the physical value of the pion mass.