Primordial Black Hole as a Source of the Boost Factor

TL;DR

This paper proposes that primordial black holes can seed ultracompact minihalos that enhance WIMP annihilation, potentially explaining cosmic ray excesses and offering testable predictions through gamma-ray and gravitational-wave observations.

Contribution

It introduces a novel scenario where PBH-seeded UCMHs significantly boost WIMP annihilation, explaining cosmic ray anomalies without conflicting with existing constraints.

Findings

Boost factor can reach up to 10^5.

UCMHs can account for positron/electron excesses observed by PAMELA/Fermi.

Scenario is testable via gamma-ray and gravitational-wave experiments.

Abstract

Primordial black holes (PBHs) accumulate weakly interacting massive particles (WIMPs) around them and form ultracompact minihalos (UCMHs), if the WIMP is a dominant component of the dark matter (DM). In this paper, we discuss that the UCMHs seeded by the PBHs with sub-earth mass enhance the WIMP annihilation in the present Universe and can successfully explain the positron and/or electron excess in cosmic ray observed by PAMELA/Fermi experiments. The signal is very similar to that from a decaying dark matter, which can explain the PAMELA and/or Fermi anomaly without conflict with any constraints as long as the decay mode is proper. In this scenario, the boost factor can be as large as 10^5. In addition, we discuss testability of our scenario by gamma-ray point source and gravitational-wave experiments.