An accurate model for the primordial black hole mass distribution from a peak in the power spectrum

TL;DR

This paper refines models of primordial black hole mass distribution from peaks in the power spectrum, emphasizing critical collapse effects and proposing alternative skewed models for better accuracy in data analysis.

Contribution

It demonstrates the limitations of the lognormal model for narrow peaks and introduces skew-lognormal and generalized models as improved alternatives.

Findings

Critical collapse influences the minimum width of the mass distribution.

Lognormal model is insufficient for narrow peaks; alternative models perform better.

Proposed models enable efficient and accurate analysis of PBH data.

Abstract

We examine the shape of the primordial black hole mass distribution arising from a peak in the primordial power spectrum. In light of improvements to the modelling, we revisit the claim that the effects of critical collapse produce a distribution that is not described by the commonly assumed lognormal, showing that this conclusion remains valid, particularly for narrow peaks where the shape of the mass distribution is insensitive to the peak properties and critical collapse determines a minimum width. We propose some alternative models that may better describe the shape, both for the narrow peak case and for much broader peaks where the effect of the peak shape is significant. We highlight the skew-lognormal and a generalised model motivated by the physics of critical collapse as the best of these possible alternatives. These models can be used as an accurate and fast approximation to the numerically calculated mass distribution, allowing for efficient implementation in an MCMC analysis. We advocate the use of one of these two models instead of the lognormal with sufficiently accurate data, such as future LIGO-Virgo observations, or when considering strongly mass dependent constraints on the PBH abundance.