SOFT PHOTON PRODUCTION FROM QUARK–GLUON PLASMA AND CANCELLATION OF MASS SINGULARITY

It has recently been reported that the production rate of soft real photons from a hot quark–gluon plasma exhibits unscreened mass singularities even within the hard-thermal-loop resummation scheme. It is shown that there exist another diagrams that cancel the singular contribution, in accordance with the general theorem of absence of mass singularities in thermal reaction rates, provided one sums over the set of all degenerate initial and final states. An interpretation of the relevant diagrams is given in terms of physical processes taking place in the quark–gluon plasma. The mechanism of canceling mass singularities in this example is similar to the one in vacuum theory.