Nucleon mass and sigma term from lattice QCD with two light fermion flavors

We analyze Nf=2 nucleon mass data with respect to their dependence on the pion mass down to mπ=157 MeV and compare it with predictions from covariant baryon chiral perturbation theory (BChPT). A novel feature of our approach is that we fit the nucleon mass data simultaneously with the directly obtained pion–nucleon σ-term. Our lattice data below mπ=435 MeV is well described by O(p4) BChPT and we find σ=37(8)(6) MeV for the σ-term at the physical point. Using the nucleon mass to set the scale we obtain a Sommer parameter of r0=0.501(10)(11) fm.