TEMPERATURE-DEPENDENT PARTICLE-PRODUCTION AND STIMULATED EMISSIONS BY EXTERNAL SOURCES

Exact solutions for transition amplitudes for particle production and stimulated emission by external sources are derived for finite temperatures. More precisely, we obtain the expressions for amplitudes for the emission of an arbitrary number of particles by the sources, and corresponding stimulated emission processes, when one is dealing with a generalized multiparticle state (rather than the vacuum) at finite temperatures. The solutions are given for spin-O, massive and massless (photons) spin-1, and spin-1/2 particles. As applications, we study the process: photon --> any photons, in the presence of a strong external electromagnetic current, with the net release of a specified energy, and work out the power radiated by a given electromagnetic current distribution, all at finite temperatures. The latter application includes the radiation emitted by a point charged particle at T not-equal 0 as a special case.