Primordial black holes and gravitational waves induced by exponential-tailed perturbations

TL;DR

This paper explores how exponential-tailed non-Gaussian primordial fluctuations influence the gravitational wave signals induced by primordial black holes, assessing their detectability by future GW observatories like LISA and DECIGO.

Contribution

It provides a detailed analysis of the stochastic gravitational wave spectrum considering exponential-tail non-Gaussianity, using a diagrammatic approach to relate PBH abundance and GW signals.

Findings

GW amplitude slightly lower than Gaussian case but detectable by LISA

Non-Gaussianity affects high-frequency GW features

Potential to probe non-Gaussianity with future GW detectors

Abstract

Primordial black holes (PBHs) whose masses are in $\sim[10^{-15}M_\odot,10^{-11}M_{\odot}]$ have been extensively studied as a candidate of whole dark matter (DM). One of the probes to test such a PBH-DM scenario is scalar-induced stochastic gravitational waves (GWs) accompanied with the enhanced primordial fluctuations to form the PBHs with frequency peaked in the mHz band being targeted by the LISA mission. In order to utilize the stochastic GWs for checking the PBH-DM scenario, it needs to exactly relate the PBH abundance and the amplitude of the GWs spectrum. Recently in Kitajima et al., the impact of the non-Gaussianity of the enhanced primordial curvature perturbations on the PBH abundance has been investigated based on the peak theory, and they found that a specific non-Gaussian feature called the exponential tail significantly increases the PBH abundance compared with the Gaussian case. In this work, we investigate the spectrum of the induced stochastic GWs associated with PBH DM in the exponential-tail case. In order to take into account the non-Gaussianity properly, we employ the diagrammatic approach for the calculation of the spectrum. We find that the amplitude of the stochastic GW spectrum is slightly lower than the one for the Gaussian case, but it can still be detectable with the LISA sensitivity. We also find that the non-Gaussian contribution can appear on the high-frequency side through their complicated momentum configurations. Although this feature emerges under the LISA sensitivity, it might be possible to obtain information about the non-Gaussianity from GW observation with a deeper sensitivity such as the DECIGO mission.