CANCELLATION OF INFRARED DIVERGENCES AT FINITE-TEMPERATURE

We consider a typical hard scattering process in a heat bath of photon s and electrons at temperature, T, in finite temperature QED. We show that the infrared pieces of both the real and virtual parts of the cro ss section factorise; these can be exponentiated and cancel between ea ch other to all orders in perturbation theory. Hence the Bloch-Nordsie ck theorem remains valid for such processes at non-zero temperature as well. We use the technique of Grammer and Yennie to give a prescripti on for the extraction of the infrared divergent parts and for the form of the finite remainder. Symmetry arguments are used to show the fini teness of new terms arising in the T not equal 0 part of the computati on. (C) 1998 Academic Press.