Simulation of Primordial Black Holes with large negative non-Gaussianity

TL;DR

This paper performs numerical simulations of primordial black hole formation considering negative non-Gaussianity, revealing new formation thresholds and challenging previous analytical predictions.

Contribution

It introduces numerical analysis of PBH formation with negative non-Gaussianity, providing refined threshold estimates and identifying PBH formation in previously unexpected parameter ranges.

Findings

PBH formation occurs for $f_{NL} \, \lesssim -0.336$.

Numerical thresholds differ from previous analytical estimates.

An alternative analytical estimate closely matches numerical results for $f_{NL} \, \gtrsim -1$.

Abstract

In this work, we have performed numerical simulations of primordial black hole (PBH) formation in the Friedman-Lema\^itre-Robertson-Walker universe filled by radiation fluid, introducing the local-type non-Gaussianity to the primordial curvature fluctuation. We have compared the numerical results from simulations with previous analytical estimations on the threshold value for PBH formation done in the previous paper arXiv:2109.00791, particularly for negative values of the non-linearity parameter $f_{\rm NL}$. Our numerical results show the existence of PBH formation of (the so-called) type I also in the case $f_{\rm NL} \lesssim -0.336$, which was not found in the previous analytical expectations using the critical averaged compaction function. In particular, although the universal value for the averaged critical compaction function $\bar{\mathcal{C}}_{c}=2/5$ found previously in the literature is not satisfied for all the profiles considered in this work, an alternative direct analytical estimate has been found to be roughly accurate to estimate the thresholds, which gives the value of the critical averaged density with a few $\%$ deviation from the numerical one for $f_{\rm NL}\gtrsim -1$.