NANOGrav Hints to Primordial Black Holes as Dark Matter

TL;DR

This paper suggests that the gravitational wave background detected by NANOGrav could be explained by primordial black holes formed during inflation, which might also constitute all dark matter and be detectable by LISA.

Contribution

It proposes a novel explanation linking NANOGrav's gravitational wave signal to primordial black holes formed during inflation, predicting their mass range and detectability by LISA.

Findings

Primordial black holes could account for all dark matter.

The gravitational wave background is consistent with black hole formation during inflation.

LISA could detect the predicted gravitational wave background.

Abstract

The NANOGrav Collaboration has recently published a strong evidence for a stochastic common-spectrum process that may be interpreted as a stochastic gravitational wave background. We show that such a signal can be explained by second-order gravitational waves produced during the formation of primordial black holes from the collapse of sizeable scalar perturbations generated during inflation. This possibility has two predictions: $i$) the primordial black holes may comprise the totality of the dark matter with the dominant contribution to their mass function falling in the range $(10^{-15}\div 10^{-11}) M_\odot$ and $ii$) the gravitational wave stochastic background will be seen as well by the LISA experiment.