Primordial Black Holes as a dark matter candidate

TL;DR

This paper reviews the potential of primordial black holes as dark matter candidates, discussing their formation, current constraints, and open questions as of 2020.

Contribution

It provides a concise overview of the formation mechanisms, observational constraints, and unresolved issues regarding PBHs as dark matter.

Findings

PBHs formed from inflationary density perturbations are a viable dark matter candidate.

Current observational constraints limit the abundance of PBHs in certain mass ranges.

Open questions remain about the formation processes and detection prospects of PBHs.

Abstract

The detection of gravitational waves from mergers of tens of Solar mass black hole binaries has led to a surge in interest in Primordial Black Holes (PBHs) as a dark matter candidate. We aim to provide a (relatively) concise overview of the status of PBHs as a dark matter candidate, circa Summer 2020. First we review the formation of PBHs in the early Universe, focusing mainly on PBHs formed via the collapse of large density perturbations generated by inflation. Then we review the various current and future constraints on the present day abundance of PBHs. We conclude with a discussion of the key open questions in this field.