Gravitational waves induced by the local-type non-Gaussian curvature perturbations

TL;DR

This paper analyzes how local-type non-Gaussian curvature perturbations affect scalar-induced gravitational waves (SIGWs), revealing that non-Gaussianity can suppress SIGW signals and impact their detectability by LISA, thus influencing primordial black hole dark matter scenarios.

Contribution

It provides a comprehensive analysis of third-order non-Gaussian effects on SIGWs, showing their impact on the amplitude and spectral slope, which was not fully explored before.

Findings

SIGWs exhibit a log-dependent infrared slope due to non-Gaussianity.

Amplitude of SIGWs can be suppressed by several orders of magnitude.

Null detection by LISA does not exclude PBHs as dark matter candidates.

Abstract

The current observational constraints still leave a substantial mass window $\sim [10^{-16},10^{-14}] \cup [10^{-13},10^{-12}] M_\odot$ for primordial black holes (PBHs) representing all of dark matter (DM) in our Universe. The gravitational waves (GWs) induced by the curvature perturbations are inevitably generated during the formation of these PBHs, and fall in the frequency band of LISA. Such scalar induced gravitational waves (SIGWs) are supposed to be definitely detected by LISA even when the second-order local-type non-Gaussianity characterized by the parameter $F_{\rm NL}$ is taken into account. In this letter, we give a comprehensive analysis of the GWs induced by the local-type non-Gaussian curvature perturbations up to the third-order denoted by the non-linear parameter $G_{\rm NL}$, and find that a log-dependent slope of SIGWs in the infrared region is generically predicted and the amplitude of SIGWs can be further suppressed by several orders of magnitude. Therefore, the null-detection of SIGWs by LISA cannot rule out the possibility of PBHs making up all of DM.