Thermal photons and lepton pairs from quark gluon plasma and hot hadronic matter

The formulation of the real and virtual photon production rate from strongl y interacting matter is presented in the framework of finite temperature fi eld theory. Th changes in the hadronic spectral function induced by tempera ture are discussed within the ambit of the Walecka type model, gauged linea r and non-linear sigma models. hidden local symmetry approach, and QCD sum rule approach. The possibility of observing the direct thermal photon and l epton pairs from quark gluon plasma has been contrasted with those from hot hadronic matter with and without medium effects Ibr various mass variation scenarios. At SPS energies, in-medium effects of different magnitude on th e hadronic properties for the Walecka model. Brown-Rho scaling. and Nambu s caling scenarios are conspicuously visible through the low invariant mass d istribution of dileptons and transverse momentum spectra of photons. Howeve r at RHIC energies the thermal photon (dilepton) spectra originating from q uark gluon plasma overshines those from hadronic matter for large transvers e momentum (invariant mass) irrespective of the models used for evaluating the finite temperature effects on the hadronic pn,properties. It is thus ex pected that at both RHIC and LHC energies the formation of quark gluon plas ma in the initial stages may indeed turn out to be a realistic scenario. (C ) 2000 Academic Press.