Navigating the asteroid field: New evaporation constraints for primordial black holes as dark matter

Abstract

Primordial black holes (PBHs) in the asteroid-mass range (10−17–10−12) M almost entirely escape constraints as dark matter candidates. In the early universe, however, the Schwarzschild metric is no longer applicable and we must carefully consider PBH metrics with a proper cosmological embedding. In particular, the Thakurta solution stands out as perhaps the most adequate such solution. Notably, the Thakurta metric contains a timedependent apparent horizon, proportional to the cosmological scale-factor. We show that this implies the PBHs are hotter than in the standard Schwarzschild case, and so evaporate significantly faster via Hawking radiation. By matter-radiation equality, PBHs up to masses of ∼ 10−12 M have totally evaporated, and so cannot be a viable dark matter candidate. ar X iv :2 10 3. 02 81 5v 1 [ as tr oph .C O ] 4 M ar 2 02 1