Primordial black hole formation by vacuum bubbles II

TL;DR

This paper explores a new mechanism for primordial black hole formation via vacuum bubbles nucleating during inflation and interacting with radiation only through gravity, leading to diverse mass spectra potentially explaining various black hole observations.

Contribution

It extends previous models by considering gravitational interactions of vacuum bubbles with radiation, revealing diverse black hole mass spectra and implications for dark matter and observed black holes.

Findings

Black holes can form in subcritical or supercritical regimes.

Black hole mass spectra can be wide or narrow, with possible dual peaks.

Black holes from this mechanism could explain LIGO/Virgo detections and dark matter.

Abstract

The discoveries of LIGO/Virgo black holes in recent years have revitalized the study of primordial black holes. In this work, we investigate a mechanism where primordial black holes are formed by vacuum bubbles that randomly nucleate during inflation through quantum tunneling. After inflation, these bubbles typically run into the ambient radiation fluid with a large Lorentz factor. In our previous work, we assumed the bubble fields are strongly coupled to the standard model particles so that the bubble wall is impermeable. Here we complete this picture by considering bubbles interacting with the fluid only through gravity. By studying the scenario in several limits, we found that black holes could form in either subcritical or supercritical regime. Depending on the model parameters, the resulting mass spectrum of the black holes could be wide or narrow, and may develop two peaks separated by a large mass range. With different spectra, these black holes may account for the LIGO/Virgo black holes, supermassive black holes, and may play an important role in dark matter.