Gravitational waves from type II axion-like curvaton model and its implication for NANOGrav result

TL;DR

This paper explores a type II axion-like curvaton model that can generate gravitational waves consistent with NANOGrav observations and account for black hole mergers detected by LIGO-Virgo, by producing a broad spectrum of density perturbations.

Contribution

It introduces an improved treatment of non-Gaussianity in the curvaton model, demonstrating its ability to explain both NANOGrav signals and LIGO-Virgo black hole events.

Findings

The model produces a broad power spectrum of density perturbations.

It can simultaneously explain NANOGrav gravitational wave signals and LIGO-Virgo black hole mergers.

Enhanced non-Gaussianity treatment improves amplitude estimates of induced GWs.

Abstract

The recent report of NANOGrav is gathering attention since its signal can be explained by the stochastic gravitational waves (GWs) with $\Omega_{\rm GW}\sim 10^{-9}$ at $f\sim 10^{-8}$Hz. The PBH formation scenario is one of the candidates for the NANOGrav signal, which can simultaneously explain the observed $30 M_\odot$ black holes in the binary merger events in LIGO-Virgo collaboration. We focus on the type II axion-like curvaton model of the PBH formation. In type II model the complex field whose phase part is the axion rolls down from the origin of the potential. It is found that type II model achieves the broad power spectrum of the density perturbations and can simultaneously explain the LIGO-Virgo events and the NANOGrav signal. We also improve the treatment of the non-Gaussianity of perturbations in our model to accurately estimate the amplitude of the induced GWs.