Searching for Dark Matter Constituents with Many Solar Masses

TL;DR

This paper explores the possibility that dark matter could consist of primordial black holes with masses between hundreds and hundreds of thousands of solar masses, challenging the focus on axions and WIMPs.

Contribution

It argues that high-mass dark matter candidates are likely primordial black holes and reviews observational strategies for detecting them.

Findings

Primordial black holes are viable dark matter candidates at high masses.

Current observational constraints suggest intermediate mass black holes as dark matter.

Extended microlensing experiments are promising for detecting these black holes.

Abstract

Searches for dark matter (DM) constituents are presently mainly focused on axions and WIMPs despite the fact that far higher mass constituents are viable. We discuss and dispute whether axions exist and those arguments for WIMPs which arise from electroweak supersymmetry. We focus on the highest possible masses and argue that, since if they constitute all DM they cannot be baryonic, they must uniquely be primordial black holes. Observational constraints require them to be of intermediate masses mostly between a hundred and a hundred thousand solar masses. Known search strategies include wide binaries, CMB distortion and, most promisingly, extended microlensing experiments.