  We show that in the presence of a chemical potential, black hole evaporation
generates baryon number. If the inflaton or Ricci scalar is derivatively
coupled to the B-L current, the expansion of the universe acts as a chemical
potential and splits the energy levels of particles and their anti-particles.
The asymmetric Hawking radiation of primordial black holes can thus be used to
generate a B-L asymmetry. If dark matter is produced by the same mechanism, the
coincidence between the mass density of visible and dark matter can be
naturally explained.
