Four-point spectral functions and Ward identities in hot QED - art. no. 085013

We derive spectral representations for the different components of the four -point function at finite temperature in the real time formalism in terms o f five real spectral densities. We explicitly calculate all these functions in QED in the hard thermal loop approximation. The Ward identities obeyed by the one-loop three- and four-point functions in real lime and their spec tral functions are derived. We compare our results with those derived previ ously in the imaginary-time formalism for retarded functions in hot QCD, an d we discuss the generalization of our results to non-equilibrium situation s.