Initial clustering and the primordial black hole merger rate

TL;DR

This paper investigates how local non-Gaussianity influences the initial clustering, mass distribution, and merger rates of primordial black holes, revealing significant effects even with small non-Gaussianity levels.

Contribution

It introduces the impact of local non-Gaussianity on PBH clustering and mass function, highlighting the resulting increase in merger rates and associated uncertainties.

Findings

Non-Gaussianity enhances PBH clustering and merger rates.

PBH mass function shifts toward higher masses.

Strong clustering introduces large uncertainties in merger rate estimates.

Abstract

If the primordial curvature perturbation followed a Gaussian distribution, primordial black holes (PBHs) will be Poisson distributed with no additional clustering. We consider local non-Gaussianity and its impact on the initial PBH clustering and mass function due to mode coupling between long and short wavelength modes. We show that even a small amount of non-Gaussianity results in a significant enhancement on the PBH initial clustering and subsequent merger rate and that the PBH mass function shifts to higher mass PBHs. However, as the clustering becomes strong, the local number density of PBHs becomes large, leading to a large theoretical uncertainty in the merger rate.