Chiral extrapolation of nucleon mass and axial coupling g_A

We analyze the quark mass dependence of the nucleon mass M_N and the axial-vector coupling constant g_A in the framework of the effective low-energy theory of QCD in the one-nucleon sector and two flavor case, namely SU(2) Baryon Chiral Perturbation Theory (BChPT). The relevant formulae are compared with those obtained using an extension of this effective field theory which explicitly includes Δ (1232) degrees of freedom. A numerical analysis is performed taking as input lattice QCD data. It turns out that in order to obtain at the one-loop level an interpolating function able to connect the physical point with present lattice data at relatively large pion masses, the inclusion of explicit Δ (1232) degrees of freedom is not decisive for the nucleon mass but crucial for g_A.