Nucleons at finite temperature.

The nucleon mass shift is calculated using chiral counting arguments and a virial expansion, without and with the ∆. At all temperatures, the mass shift and damping rate are dominated by the ∆. Our results are compared with the empirical analysis of Leutwyler and Smilga, as well as results from heavy baryon chiral perturbation theory in the large N c (number of color) limit. We show that unitarity implies that the concepts of thermal shifts are process dependent.