Calculational rules for finite temperature reaction rates

Systematic calculational rules are found for evaluating the reaction rate of a generic process taking place in a thermal reservoir in equilibrium. The rules are formulated in a diagrammatic representation within the framework of a real-time thermal field theory. It becomes clear how each 'forward' diagram can be cut; thus the finite temperature generalization of the Cutkosky (or cutting) rules is settled. The relationship is clarified between our diagrammatic rules and those for finding the imaginary part of the relevant 'forward' amplitude established by Kobes and Semenoff; the latter is shown to contain different reaction rates. (orig.)