The impact of non-Gaussianity when searching for Primordial Black Holes with LISA

TL;DR

This paper investigates how non-Gaussian primordial density perturbations and astrophysical foregrounds affect LISA's ability to detect gravitational waves linked to primordial black hole dark matter, revealing significant uncertainties in probing the asteroid-mass PBH window.

Contribution

It demonstrates that non-Gaussianity and foregrounds weaken LISA's constraints on primordial black hole dark matter, providing a reevaluation of detection prospects considering these effects.

Findings

Uncertainties in $f_{NL}$ significantly impact PBH abundance estimates.

Astrophysical foregrounds reduce LISA's sensitivity to SIGWs from PBHs.

Non-Gaussianity introduces substantial variability in primordial black hole detection prospects.

Abstract

LISA can observe cosmological millihertz (mHz) gravitational wave (GW) backgrounds that may offer a decisive test for asteroid-mass primordial black hole (PBH) dark matter (DM). In standard scenarios, failing to detect a scalar-induced gravitational wave (SIGW) background would exclude the last viable window for PBH DM formed through critical collapse. We show that this conclusion becomes much weaker in the presence of astrophysical foregrounds and strongly non-Gaussian primordial density perturbations, by studying how these phenomena affect the link between SIGWs and PBHs, and reevaluate LISA's sensitivity to asteroid-mass PBHs. In addition, we analyse the interplay between PBHs and SIGWs to gain further insights into the nature of primordial non-Gaussianity. We find that uncertainties in $f_{\rm NL}$ can induce substantial uncertainties in the PBH abundance, which ultimately limits LISA's capacity to fully probe the asteroid-mass PBH DM window.