Primordial Black Holes from Confinement

TL;DR

This paper proposes a novel mechanism for primordial black hole formation involving confining gauge theories and inflation, potentially explaining dark matter and supermassive black holes, with observable gravitational wave signatures.

Contribution

It introduces a new formation process for primordial black holes via confinement dynamics, applicable to generic theories including QCD, and links to observable gravitational waves.

Findings

Black holes can form from confined quark pairs after inflation.

Produced black holes can be lighter and higher spin than standard models.

Gravitational wave signals are within the range of recent NANOGrav data.

Abstract

A mechanism for the formation of primordial black holes is proposed. Here, heavy quarks of a confining gauge theory produced by de Sitter fluctuations are pushed apart by inflation and get confined after horizon re-entry. The large amount of energy stored in the colour flux tubes connecting the quark pair leads to black-hole formation. These are much lighter and can be of higher spin than those produced by standard collapse of horizon-size inflationary overdensities. Other difficulties exhibited by such mechanisms are also avoided. Phenomenological features of the new mechanism are discussed as well as accounting for both the entirety of the dark matter and the supermassive black holes in the galactic centres. Under proper conditions, the mechanism can be realised in a generic confinement theory, including ordinary QCD. We discuss a possible string-theoretic realisation via $D$-branes. Interestingly, for conservative values of the string scale, the produced gravity waves are within the range of recent NANOGrav data. Simple generalisations of the mechanism allow for the existence of a significant scalar component of gravity waves with distinct observational signatures.