Implications for the non-Gaussianity of primordial gravitational waves from pulsar timing arrays

TL;DR

This paper explores how tensor non-Gaussianity in primordial gravitational waves affects their spectrum and uses pulsar timing array data to constrain non-Gaussianity parameters, providing new insights into early Universe physics.

Contribution

It introduces the first constraints on tensor non-Gaussianity from PTA data and discusses the implications for inflationary models and early Universe dynamics.

Findings

Constraint |F_NL| 7.97 for log-normal spectrum

Moderate non-Gaussianity causes significant deviations from standard predictions

Future GW observatories will improve constraints on tensor non-Gaussianity

Abstract

The detection of a stochastic signal by recent pulsar timing array (PTA) collaborations, including NANOGrav, PPTA, EPTA+InPTA, CPTA and MPTA, has opened a new window to explore gravitational waves (GWs) at nanohertz frequencies. Motivated by the possibility that such a signal could arise from primordial gravitational waves (PGWs), we investigate the implications of tensor non-Gaussianity for the PGW power spectrum. Utilizing PTA data sets, we provide constraints on local-type tensor non-Gaussianity parameter ${F}_{\mathrm{NL}}$. We find $|{F}_{\mathrm{NL}}|\lesssim 7.97$ for a log-normal PGW power spectrum. Our analysis reveals that even moderate tensor non-Gaussianity can lead to significant deviations from standard predictions, thereby offering a novel means to test inflationary scenarios and probe the underlying dynamics of the early Universe. Future multi-band GW observatories, such as LISA, Taiji, and TianQin, will be instrumental in complementing these efforts and further refining our understanding of tensor non-Gaussianity.