The nucleon mass and pion-nucleon sigma term from a chiral analysis of Nf = 2 lattice QCD world data

Abstract

We investigate the pion-mass dependence of the nucleon mass within the covariant SU(2) baryon chiral perturbation theory up to order p4 with and without explicit Δ (1232) degrees of freedom. We fit lattice QCD data from several collaborations for 2 and 2+1 flavor ensembles. Here, we emphasize our Nf = 2 study where the inclusion the Δ (1232) contributions stabilizes the fits. We correct for finite volume and spacing effects, set independently the lattice QCD scale by a Sommer-scale of r0 = 0.493(23) fm and also include one σπN lQCD data point at Mπ ≈ 290 MeV. We obtain low-energy constants of natural size which are compatible with the rather linear pion-mass dependence observed in lattice QCD. We report a value of σπN = 41(5)(4) MeV for the 2 flavor case and σπN = 52(3)(8) MeV for 2+1 flavors.