Abstract

Between the end of Inflation and primordial nucleosynthesis, the Universe goes through non-linear, non-perturbative and out-of-equilibrium stages, like Reheating or Phase Transitions (PhT). In particular, the spatial distribution of the fields develops inhomogeneities during these complicated periods, producing Gravitational Waves (GW) copiously. This seminar will thus be devoted to the details of the generation of such primordial GW backgrounds, studying global and gauge scenarios of Reheating and PhT’s, and considering both sub- and super-horizon scales. GW decouple upon production and propagate unimpeded carrying invaluable information about the high energy process that generated them. Therefore, the detection of this gravitational radiation would open a new observational window into the very early Universe. Moreover, these GW backgrounds may easily have a much greater amplitude than the GW background expected from Inflation (and might even mimic the spectrum of the latter), so a correct understanding of them seems timely.