Searching for Dark Matter Constituents with Many Solar Masses

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.