DAMPING OF A YUKAWA FERMION AT FINITE-TEMPERATURE

The damping of a massless fermion coupled to a massless scalar particle at finite temperature is considered using the Braaten-Pisarski resummation technique. First the hard thermal loop diagrams of this theory are extracted and effective Green's functions are constructed. Using these effective Green's functions the damping rate of a soft Yukawa fermion is calculated. This rate provides the simplest example for the damping of a soft particle. To leading order it is proportional to g(2)T, whereas the one of a hard fermion is of higher order.