NANOGrav Hints on Planet-Mass Primordial Black Holes

TL;DR

This paper suggests that the gravitational wave background detected by NANOGrav could be caused by primordial black holes formed from peaked curvature perturbations, linking GW observations to PBH dark matter candidates.

Contribution

It proposes a novel connection between NANOGrav's gravitational wave signals and the existence of planet-mass primordial black holes from a specific early universe scenario.

Findings

GW background amplitude and index imply a dust-like post-inflationary era.

Predicted PBHs could explain OGLE's ultrashort-timescale microlensing events.

The model links GW observations to primordial black hole dark matter.

Abstract

Recently, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) claimed the detection of a stochastic common-spectrum process of the pulsar timing array (PTA) time residuals from their 12.5 year data, which might be the first detection of the stochastic background of gravitational waves (GWs). We show that the amplitude and the power index of such waves imply that they could be the secondary GWs induced by the peaked curvature perturbation with a dust-like post inflationary era with $-0.091\lesssim w\lesssim0.048$. Such stochastic background of GWs naturally predicts substantial existence of planet-mass primordial black holes (PBHs), which can be the lensing objects for the ultrashort-timescale microlensing events observed by the Optical Gravitational Lensing Experiment (OGLE).