Speaker
Description
Gravitational waves are naturally sourced by hydrodynamical fluctuations in a thermal medium, as the one that filled the universe before recombination. Since the corresponding gravitational wave spectrum is expected to show rapid growth at high frequencies, unprecedented prospects to detect these signals may be offered by proposed interferometers. While the spectral shape is well understood, the peak amplitude is set by the plasma temperature at emission. To estimate a model-independent upper bound for the maximal temperature reached after inflation, the late stage of the reheating process may be captured by a two-component approach, in which a self-interacting plasma has already attained local equilibrium, while the inflaton field is still far from equilibrium. We describe the foundations of such an approach, and also discuss the implications for the curvature power spectrum, which can in principle be studied both in a linear and non-linear regime.
