Super-critical primordial black hole formation via delayed first-order electroweak phase transition

TL;DR

This paper investigates how delayed first-order electroweak phase transitions can lead to the formation of super-critical primordial black holes through bubble dynamics, updating parameter constraints for new physics models.

Contribution

It introduces a new PBH formation criterion based on timescales and demonstrates formation via numerical simulations assuming spherical false vacuum domains.

Findings

Super-critical PBHs can form from delayed EWPTs under certain conditions.

A timescale-based criterion is more effective than density fluctuation criteria.

Updated parameter regions for new physics models are provided.

Abstract

The delay of the first-order electroweak phase transitions (EWPT) may lead to the emergence of baby universes inside wormhole structures due to the large vacuum energy density in false vacuum domains. Observers outside the false vacuum domains observe them as primordial black holes (PBHs), categorized as super-critical PBHs. We specifically investigate the dynamics of PBH formation due to delayed first-order EWPTs by solving the equations of bubble wall dynamics. We numerically confirm that such super-critical PBHs can be formed by the delayed first-order EWPT assuming spherically symmetric false vacuum domains with the thin-wall approximation for its boundary. Our numerical results show that a PBH formation criterion utilizing characteristic timescales is more appropriate than the conventional criterion based on density fluctuations. Employing our numerical results, we update the parameter regions of new physics models which can be explored by current and future constraints on the PBH abundance.