Constraining Mixed Dark-Matter Scenarios of WIMPs and Primordial Black Holes from CMB and 21-cm observations

TL;DR

This paper investigates how mixed dark matter scenarios involving WIMPs and primordial black holes are constrained by CMB and 21-cm observations, finding that CMB data impose very tight bounds on PBH fractions.

Contribution

It provides new bounds on the PBH fraction in mixed dark matter models using CMB data and explores the potential of 21-cm signals for further constraints.

Findings

CMB data tightly constrain PBH dark matter fraction to below 10^{-10} for certain WIMP masses.

PBH fractions can be comparable or tighter constrained than gamma-ray data.

21-cm observations could offer additional stringent constraints on PBH abundance.

Abstract

We consider the dark matter (DM) scenarios consisting of the mixture of WIMPs and PBHs and study how much fraction of the total DM can be PBHs. In such scenarios, PBHs can accrete the WIMPs and consequently enhance the heating and ionization in the intergalactic medium due to WIMP annihilations. We demonstrate that the CMB data can give the stringent bounds on the allowed PBH fraction which are comparable or even tighter than those from the gamma ray data depending on the DM masses. For instance, the MCMC likelihood analysis using the Planck CMB data leads to the bound on PBH DM fraction with respect to the total dark matter $f_{\rm PBH} \lesssim {\cal O}( 10^{-10}\sim 10^{-8})$ for the WIMP mass $m_{\chi}\sim {\cal O}(10\sim 10^3)$ GeV with the conventional DM annihilation cross section $\langle \sigma v \rangle=3 \times 10^{-26}~\rm cm^3/s $. We also investigate the feasibility of the global 21-cm signal measurement to provide the stringent constraints on the PBH fraction.