IMPROVED HARD-THERMAL-LOOP EFFECTIVE ACTION FOR HOT QED AND QCD

The conventional results for hard thermal loops, which are the buildin g blocks of resummed perturbation theory in thermal field theories, ha ve collinear singularities when external momenta are light-like. It is shown that by taking into account asymptotic thermal masses these sin gularities are removed. The thus improved hard thermal loops can be su mmarized by compact gauge-invariant effective actions, generalizing th e ones found by Taylor and Wong, and by Braaten and Pisarski.