Black Hole Genesis of Dark Matter

TL;DR

This paper proposes a gravitational mechanism for dark matter production via primordial micro black holes, analyzing different regimes and their implications for dark matter properties and observational signatures.

Contribution

It introduces a novel, purely gravitational, IR-calculable production mechanism for dark matter involving primordial black holes and explores its various regimes and observational consequences.

Findings

Dark matter can be produced through black hole evaporation in different regimes.

Light dark matter faces free-streaming constraints, while heavy dark matter offers detection possibilities.

A predicted dark radiation component accompanies dark matter production.

Abstract

We present a purely gravitational infra-red-calculable production mechanism for dark matter (DM). The source of both the DM relic abundance and the hot Standard Model (SM) plasma is a primordial density of micro black holes (BHs), which evaporate via Hawking emission into both the dark and SM sectors. The mechanism has four qualitatively different regimes depending upon whether the BH evaporation is `fast' or `slow' relative to the initial Hubble rate, and whether the mass of the DM particle is `light' or `heavy' compared to the initial BH temperature. For each of these regimes we calculate the DM yield, $Y$, as a function of the initial state and DM mass and spin. In the `slow' regime $Y$ depends on only the initial BH mass over a wide range of initial conditions, including scenarios where the BHs are a small fraction of the initial energy density. The DM is produced with a highly non-thermal energy spectrum, leading in the `light' DM mass regime ($\sim260\,\mathrm{eV}$ and above depending on DM spin) to a strong constraint from free-streaming, but also possible observational signatures in structure formation in the spin 3/2 and 2 cases. The `heavy' regime ($\sim1.2\times 10^8\,\mathrm{GeV}$ to $M_{\mathrm{Pl}}$ depending on spin) is free of these constraints and provides new possibilities for DM detection. In all cases there is a dark radiation component predicted.