Leptogenesis in Brane-modified cosmology: Signatures in primordial gravitational waves

Abstract

We investigate the implications of brane-inspired modifications of the evolutionary history of the early universe on the process of baryogenesis via leptogenesis. A modified cosmic history alters the evolution of the Boltzmann equations governing lepton asymmetry, providing the possibility of successful leptogenesis in regions of the parameter space inaccessible in the standard cosmological scenario. Furthermore, a modified cosmic history also alters the shape of an otherwise scale-invariant spectral energy density (SED) of primary gravitational waves (PGWs) produced during inflation. This establishes a novel yet indirect probe of high scale leptogenesis scenarios through the observation of the SED of PGWs via future observations. We consider two scenarios in this work with single and multiple epochs of stiff equation of state(s) after inflation and before the epoch of radiation domination. We identify the parameter space where successful leptogenesis is possible, along with the possible observability of the PGWs, hence providing an indirect window into this leptogenesis scenario through PGWs.