Primordial Black Holes as Dark Matter: New Formation Scenarios and Astrophysical Effects

Abstract Primordial black holes are a viable dark matter candidate. They decay via Hawking evaporation. Energetic particles from the Hawking radiation interact with interstellar gas, depositing their energy as heat and ionization. For a sufficiently high Hawking temperature, fast electrons produced by black holes deposit a substantial fraction of energy as heat through the Coulomb interaction. Using the dwarf galaxy Leo T, we place an upper bound on the fraction of primordial black hole dark matter. For M < 5 × 10−17M⊙, our bound is competitive with or stronger than other bounds.

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Primordial black holes from the QCD epoch: linking dark matter, baryogenesis, and anthropic selection

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3726 ◽

2020 ◽

Vol 501 (1) ◽

pp. 1426-1439

Author(s):

Bernard Carr ◽

Sebastien Clesse ◽

Juan García-Bellido

Keyword(s):

Black Holes ◽

Dark Matter ◽

Selection Effect ◽

Mass Function ◽

Baryon Asymmetry ◽

Primordial Black Holes ◽

Cosmological Horizon ◽

Chandrasekhar Limit ◽

The Universe ◽

Characteristic Mass

ABSTRACT 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 ∼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 hotspot 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 that 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.

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