FINITE-TEMPERATURE REACTION RATES AND THEIR INFRARED STRUCTURE

A set of diagrammatic algorithms is presented for evaluating the reaction rate of a generic process taking place in a heat bath in thermal equilibrium. This is a finite temperature genaralization of the Cutkosky or cutting rules at zero temperature. It is shown that the imaginary part of a forward amplitude in real-time thermal field theory, for which Kobes and Semenoff have established the diagrammatic rules, contains different reaction rates. Also made is an analysis of the infrared finiteness of the reaction rates.