Non-particle dark matter

TL;DR

This paper introduces non-particle dark matter, especially primordial black holes, discussing their formation, properties, observational probes, and key open questions in the field.

Contribution

It provides a comprehensive pedagogical overview of primordial black holes as non-particle dark matter candidates, including their formation mechanisms and observational constraints.

Findings

Primordial black holes can form from early Universe density perturbations.

PBHs are viable dark matter candidates under certain conditions.

Observational methods can constrain PBH abundance and properties.

Abstract

We provide a pedagogical introduction to non-particle dark matter, focused on primordial black holes (PBHs), black holes that may form in the early Universe from large overdensities. First, we outline the key properties of PBHs and how they meet the requirements to be a dark matter candidate. We then overview how PBHs can form, in particular from the collapse of large density perturbations generated by inflation (a proposed period of accelerated expansion in the early Universe). Next, we describe how PBHs can be probed by observations. Finally, we conclude with a summary focused on the key open questions in the field.