Speaker
Description
A variety of mechanisms in the early Universe lead to the generation of gravitational waves (GWs). In this talk, I will present a novel source of GWs generated by vacuum fluctuations after inflation. Since gravitons are minimally coupled, their quantum creation takes place during inflation but is absent in an unperturbed Universe during the radiation-dominated epoch, as they behave as conformally invariant particles. However, the presence of inhomogeneities breaks the conformal flatness of the metric, allowing scalar metric perturbations to induce the quantum production of gravitons. The resulting GW spectrum from this mechanism peaks around the GHz frequency range, distinguishing it from other astrophysical and cosmological backgrounds and underscoring the need for detectors sensitive to these high frequencies.