# Primordial black holes as a dark matter candidate are severely constrained by the Galactic Center 511 keV gamma-ray line

## TL;DR

This paper establishes the strongest constraints to date on low-mass primordial black holes as dark matter candidates by analyzing the Galactic Center 511 keV gamma-ray line, limiting their contribution to less than 1%.

## Contribution

It introduces a novel method to constrain primordial black holes using gamma-ray observations, covering previously unconstrained mass ranges.

## Key findings

- Primordial black holes contribute less than 1% to dark matter.
- The constraints are the most stringent in the literature.
- The method probes new mass ranges not previously constrained.

## Abstract

We derive the strongest constraint on the fraction of dark matter that can be composed of low mass primordial black holes by using the observation of the Galactic Center 511 keV gamma-ray line. Primordial black holes of masses $\lesssim$ 10$^{15}$ kg will evaporate to produce $e^\pm$ pairs. The positrons will lose energy in the Galactic Center, become non-relativistic, and then annihilate with the ambient electrons. We derive robust and conservative bounds by assuming that the rate of positron injection via primordial black hole evaporation is less than what is required to explain the SPI/ INTEGRAL observation of the Galactic Center 511 keV gamma-ray line. Depending on the primordial black hole mass function and other astrophysical uncertainties, these constraints are the most stringent in the literature and show that primordial black holes contribute to less than 1\% of the dark matter density. Our technique also probes part of the mass range which was completely unconstrained by previous studies.