# Dark Radiation and Superheavy Dark Matter from Black Hole Domination

## TL;DR

This paper explores how primordial black holes in the early universe could produce dark radiation and superheavy dark matter through Hawking radiation, potentially resolving cosmological tensions and predicting observable effects.

## Contribution

It introduces a scenario where black hole domination leads to specific predictions for dark radiation and superheavy dark matter production via Hawking radiation.

## Key findings

- Dark radiation levels $ riangle N_{eff} \\sim 0.03-0.2$ for light species.
- Dark matter candidates must be very heavy, $m_{DM} > 10^{11}$ GeV.
- Predictions are within reach of upcoming CMB experiments.

## Abstract

If even a relatively small number of black holes were created in the early universe, they will constitute an increasingly large fraction of the total energy density as space expands. It is thus well-motivated to consider scenarios in which the early universe included an era in which primordial black holes dominated the total energy density. Within this context, we consider Hawking radiation as a mechanism to produce both dark radiation and dark matter. If the early universe included a black hole dominated era, we find that Hawking radiation will produce dark radiation at a level $\Delta N_{\rm eff} \sim 0.03-0.2$ for each light and decoupled species of spin 0, 1/2, or 1. This range is well suited to relax the tension between late and early-time Hubble determinations, and is within the reach of upcoming CMB experiments. The dark matter could also originate as Hawking radiation in a black hole dominated early universe, although such dark matter candidates must be very heavy ($m_{\rm DM} >10^{11}$ GeV) if they are to avoid exceeding the measured abundance.