Rescuing high-scale leptogenesis using primordial black holes

We explore the interplay between light primordial black holes (PBH) and high-scale baryogenesis, with a particular emphasis on leptogenesis. We first review a generic baryogenesis scenario where a heavy particle, X, with mass, MX, produced solely from PBH evaporation decays to generate a baryon asymmetry. We show that the viable parameter space is bounded from above by MX less than or similar to 1017 GeV and increases with decreasing MX. We demonstrate that regions of the leptogenesis parameter space, where the lightest right-handed neutrino (RHN) mass MN1 greater than or similar to 1015 GeV and neutrino mass scale m nu greater than or similar to 0.1 eV, excluded in standard cosmology due to Delta L = 2 washout processes, become viable with the assistance of light PBHs. This scenario of PBH-assisted leptogenesis occurs because the PBHs radiate RHNs via Hawking evaporation late in the Universe's evolution when the temperature of the thermal plasma is low relative to the RHN mass. Subsequently, these RHNs can decay and produce a lepton asymmetry while the washout processes are suppressed.