Thermal mass shift of nucleons

The mass shift ΔmN of a nucleon in the finite temperature pion gas is calculated in the case of an arbitrary nucleon momentum. A general formula is used which relates the in-medium mass shift Δm(E) of a particle to the real part of the forward scattering amplitude Re F(E) of this particle on the constituents of the medium and its applicability domain is formulated. The mass shift of the nucleon in thermal equilibrium with the pion gas is also calculated.