THERMAL MATTER AND RADIATION IN A GRAVITATIONAL-FIELD

We study the one-loop contributions of matter and radiation to the gra vitational polarization tensor at finite temperatures. Using the analy tically continued imaginary-time formalism, the contribution of matter is explicitly given to next-to-leading (T2) order. We obtain an exact form for the contribution of radiation fields, expressed in terms of generalized Riemann zeta functions. A general expression is derived fo r the physical polarization tensor, which is independent of the parame trization of graviton fields. We investigate the effective thermal mas ses associated with the normal modes of the corresponding graviton sel f-energy.