$\mathcal O(10) M_\odot$ primordial black holes and string axion dark matter

TL;DR

This paper explores the possibility that primordial black holes of around 10 solar masses formed during inflation could coexist with string axion dark matter, providing an alternative to WIMPs and addressing constraints from gravitational wave observations.

Contribution

It proposes a model where inflationary primordial black holes and string axion dark matter coexist, offering a new perspective on dark matter composition compatible with LIGO observations.

Findings

Primordial black holes of order 10 solar masses can be formed during inflation.

String axion can constitute all dark matter without conflicting with PBH constraints.

The model aligns with gravitational wave detections of black hole mergers.

Abstract

LIGO-Virgo collaboration has found black holes as heavy as $M \sim 30M_\odot$ through the detections of the gravitational waves emitted during their mergers. Primordial black holes (PBHs) produced by inflation could be an origin of such events. While it is tempting to presume that these PBHs constitute all Dark Matter (DM), there exists a number of constraints for PBHs with $\mathcal{O} (10) M_\odot$ which contradict with the idea of PBHs as all DM. Also, it is known that weakly interacting massive particle (WIMP) that is a common DM candidate is almost impossible to coexist with PBHs. These observations motivate us to pursue another candidate of DM. In this paper, we assume that the string axion solving the strong CP problem makes up all DM, and discuss the coexistence of string axion DM and inflationary PBHs for LIGO events.