Constraining the impact of standard model phase transitions on primordial black holes

TL;DR

This paper examines how early universe phase transitions influence primordial black hole formation, highlighting the challenges in linking standard model effects to observed black hole populations and emphasizing the importance of power spectrum parametrization.

Contribution

It provides a detailed analysis of the impact of standard model phase transitions on primordial black hole formation, considering various power spectrum shapes and parametrizations.

Findings

QCD phase transition significantly affects black hole abundance for narrow spectra.

Electroweak phase transition has negligible impact on black hole formation.

Broader spectra show greater sensitivity to phase transition effects.

Abstract

Phase transitions in the early universe lead to a reduction in the equation of state of the primordial plasma. This exponentially enhances the formation rate of primordial black holes. However, this sensitivity to the equation of state is the same that primordial black hole abundances show to the primordial curvature power spectrum amplitude. In this paper, we investigate peaked power spectra and show the challenges associated with motivating populations of primordial black holes with standard model enhancements. The parametrisation of different power spectra plays an important role in this discussion. The allowed parameter space consistent with a large QCD phase transition impact on the primordial black hole abundance differs greatly. This is particularly evident for broader spectra. We also show that, in our framework, the electroweak phase transition cannot significantly affect the overall abundance.