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,
$M_X$, produced solely from PBH evaporation decays to generate a baryon
asymmetry. We show that the viable parameter space is bounded from above by
$M_X \lesssim 10^{17}$ GeV and increases with decreasing $M_X$. We demonstrate
that regions of the leptogenesis parameter space where the lightest
right-handed neutrino (RHN) mass $M_{N_{1}}\gtrsim 10^{15}\,{\rm GeV}$ and
neutrino mass scale $m_\nu\gtrsim 0.1$ eV, excluded in standard cosmology due
to $\Delta L=2$ washout processes, becomes 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.
