Primordial black holes in non-Gaussian regimes

TL;DR

This paper investigates how local non-Gaussianity influences primordial black hole formation, revealing that small non-Gaussian effects can significantly alter abundance constraints and that truncating the distribution leads to inaccuracies.

Contribution

It provides a detailed analysis of the impact of higher-order non-Gaussianity on PBH abundance and highlights limitations of truncated models in the curvaton scenario.

Findings

PBH abundance is highly sensitive to even small non-Gaussianities.

The sign of non-linearity parameters critically affects constraints.

Truncating the probability distribution yields inaccurate PBH predictions.

Abstract

Primordial black holes (PBHs) can form in the early Universe from the collapse of rare, large density fluctuations. They have never been observed, but this fact is enough to constrain the amplitude of fluctuations on very small scales which cannot be otherwise probed. Because PBHs form only in very rare large fluctuations, the number of PBHs formed is extremely sensitive to changes in the shape of the tail of the fluctuation distribution - which depends on the amount of non-Gaussianity present. We first study how local non-Gaussianity of arbitrary size up to fifth order affects the abundance and constraints from PBHs, finding that they depend strongly on even small amounts of non-Gaussianity and the upper bound on the allowed amplitude of the power spectrum can vary by several orders of magnitude. The sign of the non-linearity parameters (f_{NL}, g_{NL}, etc) are particularly important. We also study the abundance and constraints from PBHs in the curvaton scenario, in which case the complete non-linear probability distribution is known, and find that truncating to any given order (i.e. to order f_{NL} or g_{NL}, etc) does not give accurate results.