Stochastic gravitational wave background detection using NANOGrav 15-year data set in the context of massive gravity

TL;DR

This paper explores whether a massive gravity model can explain the NANOGrav 15-year gravitational wave background detection, analyzing parameter spaces that fit the data while respecting cosmological bounds.

Contribution

It introduces a time-dependent massive gravity model to account for the primordial gravitational wave signal observed by NANOGrav, considering constraints from BBN and CMB.

Findings

Certain parameter regions reproduce the NANOGrav signal within 1-3 standard deviations.

A suppression mechanism for high-frequency modes is necessary to satisfy BBN bounds.

Balancing the graviton mass cutoff time with cosmological constraints remains challenging.

Abstract

Convincing evidence of a stochastic gravitational wave (GW) background has been found by the NANOGrav Collaboration in the 15-year data set. From this signal, we can evaluate the possibility of its source being from the early Universe through the tensor perturbations induced by a massive spin-2 graviton field. We consider a time-dependent model of the minimal theory of massive gravity and find values of the graviton mass, mass cutoff time, and Hubble rate of inflation that amplify the energy spectra of primordial GWs sufficiently to reproduce the signal from the NANOGrav data within 1-3 standard deviation. However, a suppression mechanism for high-frequency modes must be introduced to conservatively obey the big bang nucleosynthesis (BBN) bound. While there are regions of the parameter space that reproduce the signal, it remains a challenge to simultaneously respect the BBN and cosmic microwave background bounds without making the graviton mass cutoff time too deep into the matter-dominated era.