Primordial Black Holes as a Factory of Axions: Extragalactic Photons from Axions

TL;DR

This paper explores how primordial black holes can produce axions that decay into photons, proposing a new method to estimate the resulting photon spectrum and flux, which upcoming detectors could observe.

Contribution

It introduces a novel methodology for modeling axion decay from primordial black holes over cosmological timescales, aiding future detection efforts.

Findings

Derived estimations for photon spectrum and flux from PBH-produced axions.

Showed that upcoming detectors like e-ASTROGAM could detect these signals.

Assumed monochromatic mass spectrum and isotropic PBH distribution.

Abstract

Primordial black holes (PBHs) are significant sources of axions and axion-like particles (ALPs), provided their Hawking temperature exceeds the particles' masses. Given the predominant decay of axions into photons, the enhanced photon spectrum they generate can be feasibly detected using sensitive detectors. This paper introduces a novel methodology that elucidates the decay process for particles to traverse and decay over cosmological timescales. Specifically, we derive estimations for the photon spectrum and flux, assuming a monochromatic mass spectrum and isotropic distribution for PBHs. Encouragingly, forthcoming detectors like e-ASTROGAM are well positioned to capture this signal.