Search for the non-linearities of gravitational wave background in NANOGrav 15-year data set

TL;DR

This paper investigates the potential non-Gaussian features of the gravitational wave background in NANOGrav data, finding no current evidence but highlighting the importance of future detections for understanding SGWB origins.

Contribution

It introduces a method to search for non-Gaussianity in the SGWB via non-linear effects on the overlap reduction function, focusing on a folded component parameterized by alpha.

Findings

Bayes factor indicates no evidence of non-Gaussianity in current data

Method can detect non-Gaussian features if present in future data

Results suggest non-Gaussianity detection could inform SGWB origin theories

Abstract

The recently reported signal of common red noise between pulsars by several pulsar timing array collaborations has been thought as evidence of the stochastic gravitational wave background (SGWB) due to the Helling-Downs correlation. In this Letter, we search for the non-Gaussianity of SGWB through its non-linear effect on the overlap reduction function in NANOGrav 15-year data set. In particular, we focus on a folded component to SGWB whose amplitude is quantified with a single parameter $\alpha$ in the unpolarized case. The resulting Bayes factor of $1.68 \pm 0.01$ ($1.78 \pm 0.01$ in the case of signals from SMBHBs) indicates that there is no evidence of such a non-Gaussianity of SGWB in the NANOGrav 15-year data yet. If it is detected in future PTA experiments, it will impact our understanding on the origin of the detected SGWB.