The 511 keV Excess and Primordial Black Holes

TL;DR

This paper explores whether primordial black holes could explain the 511 keV photon excess in the Milky Way, suggesting future gamma-ray telescopes can test this hypothesis by detecting related diffuse gamma-ray emissions.

Contribution

It evaluates constraints on primordial black holes as sources of positrons and proposes observational tests with upcoming gamma-ray telescopes.

Findings

Black holes of mass ~(1-4)×10^{16} g could produce the excess if they are a small dark matter component.

Current constraints from INTEGRAL, COMPTEL, and Voyager 1 are consistent with this hypothesis.

Future MeV gamma-ray telescopes can test this scenario by measuring diffuse gamma-ray emission.

Abstract

An excess of 511 keV photons has been detected from the central region of the Milky Way. It has been suggested that the positrons responsible for this signal could be produced through the Hawking evaporation of primordial black holes. After evaluating the constraints from INTEGRAL, COMPTEL, and Voyager 1, we find that black holes in mass range of $\sim(1-4)\times10^{16}$ g could potentially produce this signal if they make up a small fraction of the total dark matter density. Proposed MeV-scale gamma-ray telescopes such as AMEGO or e-ASTROGAM should be able to test this class of scenarios by measuring the diffuse gamma ray emission from the Milky Way's inner halo.