Nucleon mass, sigma term, and lattice QCD

We investigate the quark mass dependence of the nucleon mass MN. 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 p⁴. 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<0.15fm and m_πL>5. We have also restricted ourselves to data with m_π<600MeV and mₛₑₐ=mᵥₐₗ. A good interpolation function is found already at the one-loop level and chiral order p³. We show that the next-to-leading one-loop corrections are small. From the p⁴ numerical analysis we deduce the nucleon mass in the chiral limit M₀≈0.88GeV and the pion-nucleon sigma term σN=(49±3)MeV at the physical value of the pion mass.