Presentation Archive

Primordial Black Holes as Dark Matter

Bernard Carr (Queen Mary)

August 25, 2016

Abstract: The possibility that the dark matter comprises primordial black holes (PBHs) is considered, with particular emphasis on the currently allowed mass windows at 10^{16} – 10^{17}g, 10^{20} – 10^{24}g and 10 – 10^3 M[?]. The last possibility is of special interest in view of the recent detection of black-hole mergers by LIGO. All relevant constraints (lensing, dynamical, large-scale structure and accretion) are considered and various effects necessary for a precise calculation of the PBH abundance (non-Gaussianity, non-sphericity, critical collapse) are accounted for. It is difficult to put all the dark matter in PBHs if their mass function is monochromatic but this is still possible if the mass function is extended, as expected in many scenarios. A novel procedure for confronting observational constraints with an extended PBH mass spectrum is therefore introduced. The talk will focus particularly on PBHs generated by inflation, pointing out which effects in the formation process influence the mapping from the inflationary power spectrum to the PBH mass function. The possibility that Planck mass relics of evaporating PBHs provide the dark matter is also considered. This is an intriguing possibility but virtually untestable.