  Wash-in leptogenesis is a powerful mechanism to generate the baryon asymmetry
of the Universe that treats right-handed-neutrino interactions on the same
footing as electroweak sphaleron processes: as mere spectator processes acting
on the background of chemical potentials in the Standard Model plasma.
Successful wash-in leptogenesis requires this chemical background to be
CP-violating, which can be achieved by violating any of the more than ten
global charges that are conserved in the Standard Model at very high
temperatures. In this paper, we demonstrate that the primordial charge
asymmetries required for wash-in leptogenesis can be readily produced by
evaporating primordial black holes (PBHs). Our argument is based on the fact
that the Hawking radiation emitted by PBHs contains more or less any state in
the particle spectrum. Therefore, if heavy states with CP-violating decays are
present in the ultraviolet, PBH evaporation will unavoidably lead to the
production of these states. We illustrate this scenario by means of a simple
toy model where PBH evaporation leads to the production of heavy particles that
we call asymmetrons and whose decay results in a primordial charge asymmetry
for right-handed electrons, which in turn sets the initial conditions for
wash-in leptogenesis. We focus on the parameter region where the decay of the
initial thermal asymmetron abundance occurs long before PBH evaporation and
only results in a negligible primordial charge asymmetry. PBH evaporation at
later times then serves as a mechanism to resurrect the asymmetron abundance
and ensure the successful generation of the baryon asymmetry after all. We
conclude that PBHs can act as asymmetry-producing machines that grant access to
whatever CP-violating physics may be present in the ultraviolet, rekindling it
at lower energies where it can be reprocessed into a baryon asymmetry by
right-handed neutrinos.
