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

Abstract

Primordial black holes (PBHs) in the asteroid-mass range $(10^{-17}$--$10^{-12})M_{\odot }$ 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 In the early universe, however, the Schwarzschild metric is no longer applicable and we must carefully consider PBH metrics with a proper cosmological embedding.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 time-dependent 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 $\sim 10^{-12}{M}_{\odot }$ have totally evaporated, and so cannot be a viable dark matter candidate.

References in corpus (3)

• The merger rate of primordial-black-hole binaries
• Cosmological expansion and local physics
• Constraints on Primordial Black Holes by Distortions of Cosmic Microwave Background