Graviton Production by a Thermal Bath

Thermal fluctuations in the early universe plasma and in very hot astrophysical objects are an unavoidable source of gravitational waves (GW). Differently from previous studies on the subject, we approach this problem using methods based on field theory at finite temperature. Such an approach allows to probe the infrared region of the spectrum where dissipative effects are dominant. Incidentally, this region is the most interesting from the point of view of the detectability perspectives. We find significant deviations from a Planck spectrum.