Shining Primordial Black Holes

TL;DR

This paper explores a mixed dark matter model combining WIMPs and primordial black holes, analyzing gamma-ray signals from annihilation in dark minihalos around PBHs, and assessing detection prospects with current indirect searches.

Contribution

It introduces a detailed analysis of the viability of mixed WIMP and PBH dark matter scenarios, focusing on gamma-ray signals from PBH-associated minihalos and setting constraints on PBH fractions.

Findings

Potential detection of gamma-ray signals from nearby 'shining black holes' with current instruments.

Constraints on PBH fractions in dark matter based on gamma-ray observations.

Dark minihalos around PBHs can produce observable annihilation signals in the Milky Way.

Abstract

We study the well-motivated mixed dark matter (DM) scenario composed of a dominant thermal WIMP, highlighting the case of $SU(2)_L$ triplet fermion "winos", with a small fraction of primordial black holes (PBHs). After the wino kinetic decoupling, the DM particles are captured by PBHs leading to the presence of PBHs with dark minihalos in the Milky Way today. The strongest constraints for the wino DM come from the production of narrow line gamma rays from wino annihilation in the Galactic Center. We analyse in detail the viability of the mixed wino DM scenario, and determine the constraints on the fraction of DM in PBHs assuming a cored halo profile in the Milky Way. We show that already with the sensitivity of current indirect searches, there is a significant probability for detecting a gamma ray signal characteristic for the wino annihilation in a single nearby dressed PBH when $M_{\text{PBH}} \sim M_{\odot}$, which we refer to as a "shining black hole". Similar results should apply also in more general setups with ultracompact minihalos or other DM models, since the accretion of DM around large overdensities and DM annihilation are both quite generic processes.