The Magnetic Origin of Primordial Black Holes: Ultralight PBHs and Secondary GWs

TL;DR

This paper proposes a magnetogenesis-based mechanism for forming ultralight primordial black holes during inflation, which also predicts a distinctive stochastic gravitational wave background, linking early-Universe magnetism, PBHs, and GWs.

Contribution

It introduces a novel magnetogenesis model that produces ultralight PBHs without slow-roll inflation and analyzes their gravitational wave signatures.

Findings

Ultralight PBHs can form efficiently from primordial magnetic fields.

The model predicts a unique stochastic GW background linked to magnetogenesis.

Results suggest testable signatures for early-Universe magnetic fields and PBHs.

Abstract

Ultralight primordial black holes (PBHs) provide a compelling window into early-Universe cosmology. Following our earlier work, we explore a mechanism for the formation of ultralight PBHs sourced by primordial inflationary magnetic fields, without invoking an ultra-slow-roll phase of inflation. We propose a magnetogenesis model in which large curvature perturbations are induced at small scales, leading to the efficient production of ultralight PBHs across a broad mass spectrum. We analyze the phenomenological implications of these ultralight PBHs for early-Universe cosmology, particularly during reheating. We compute the resulting stochastic gravitational wave (GW) background generated by both the electromagnetic spectrum and evaporating PBHs, which exhibits distinctive features tied to the underlying magnetogenesis model parameters. Our results demonstrate that inflationary magnetic fields can serve as a viable and testable origin for ultralight PBHs, opening new avenues for probing the interplay between inflation, magnetogenesis, PBHs, and primordial gravitational waves.