Hawking Radiation of Nonrelativistic Scalars: Applications to Pion and Axion Production

TL;DR

This paper revisits Hawking radiation for nonrelativistic scalar particles like pions and axions from primordial black holes, emphasizing mass effects on production rates relevant to upcoming gamma-ray experiments.

Contribution

It provides updated greybody factors for massive scalars, highlighting significant mass corrections and the importance of non-relativistic particle production in PBH gamma-ray signals.

Findings

Mass corrections significantly alter scalar production rates.

Non-relativistic pion production impacts gamma-ray signal interpretation.

Form factor effects may suppress extended object production via Hawking radiation.

Abstract

In studying secondary gamma-ray emissions from Primordial Black Holes (PBHs), the production of scalar particles like pions and axion-like particles (ALPs) via Hawking radiation is crucial. While previous analyses assumed relativistic production, asteroid-mass PBHs, relevant to upcoming experiments like AMEGO-X, likely produce pions and ALPs non-relativistically when their masses exceed 10 MeV. To account for mass dependence in Hawking radiation, we revisit the greybody factors for massive scalars from Schwarzschild black holes, revealing significant mass corrections to particle production rates compared to the projected AMEGO-X sensitivity. We highlight the importance of considering non-relativistic $\pi^0$ production in interpreting PBH gamma-ray signals, essential for determining PBH properties. Additionally, we comment on the potential suppression of pion production due to form factor effects when producing extended objects via Hawking radiation. We also provide an example code for calculating the Hawking radiation spectrum of massive scalar particles.