Primordial black holes from the QCD epoch: Linking dark matter,
  baryogenesis and anthropic selection
  If primordial black holes (PBHs) formed at the quark-hadron epoch, their mass
must be close to the Chandrasekhar limit, this also being the characteristic
mass of stars. If they provide the dark matter (DM), the collapse fraction must
be of order the cosmological baryon-to-photon ratio $\sim 10^{-9}$, which
suggests a scenario in which a baryon asymmetry is produced efficiently in the
outgoing shock around each PBH and then propagates to the rest of the Universe.
We suggest that the temperature increase in the shock provides the ingredients
for hot spot electroweak baryogenesis. This also explains why baryons and DM
have comparable densities, the precise ratio depending on the size of the PBH
relative to the cosmological horizon at formation. The observed value of the
collapse fraction and baryon asymmetry depends on the amplitude of the
curvature fluctuations which generate the PBHs and may be explained by an
anthropic selection effect associated with the existence of galaxies. We
propose a scenario in which the quantum fluctuations of a light stochastic
spectator field during inflation generate large curvature fluctuations in some
regions, with the stochasticity of this field providing the basis for the
required selection. Finally, we identify several observational predictions of
our scenario that should be testable within the next few years. In particular,
the PBH mass function could extend to sufficiently high masses to explain the
black hole coalescences observed by LIGO/Virgo.
