Primordial black holes from long-range scalar forces and scalar radiative cooling

TL;DR

This paper proposes a novel mechanism where long-range scalar forces in the early universe lead to the formation of primordial black holes through scalar radiative cooling, potentially explaining dark matter and gravitational wave observations.

Contribution

It introduces a new formation scenario for PBHs involving scalar-mediated forces and radiation, linking dark matter properties to early universe physics.

Findings

PBHs can form during radiation era via scalar interactions

The model accounts for dark matter abundance and LIGO events

Predicts a small contribution to effective light degrees of freedom

Abstract

We describe a new scenario for the formation of primordial black holes (PBHs). In the early Universe, the long-range forces mediated by the scalar fields can lead to formation of halos of heavy particles even during the radiation-dominated era. The same interactions result in the emission of scalar radiation from the motion and close encounters of particles in such halos. Radiative cooling due the scalar radiation allows the halos to collapse to black holes. We illustrate this scenario on a simple model with fermions interacting via the Yukawa forces. The abundance and the mass function of PBHs are suitable to account for all dark matter, or for some gravitational wave events detected by LIGO. The model relates the mass of the dark-sector particles to the masses and abundance of dark matter PBHs in a way that can explain why the dark matter and the ordinary matter have similar mass densities. The model also predicts a small contribution to the number of effective light degrees of freedom, which can help reconcile different measurements of the Hubble constant.