Single Photon Production in Relativisitic Heavy Ion Collisions and Quark Hadron Phase Transition

We discuss the recent developments in the study of single photon production in relativistic heavy ion collisions. In particular their production at SPS, RHIC, and LHC energies is re-examined in view of the results of Aurenche et al which show that the rate of photon production from quark gluon plasma, evaluated at the order of two loops far exceeds the rates evaluated at one-loop level which have formed the basis of all the estimates of photons so far. We find that the production of photons from quark matter could easily out-shine those from the hadronic matter in certain ideal conditions. We further show that the earlier results lending support to the possibility of quark-hadron phase transition from the measured yield of single photons in $S+Au$ collisions at CERN SPS remain valid when an account is made for these developments, though they leave a scope for the formation of (chemically) non-equilibrated plasma.