The abundance of primordial black holes from the global 21cm signal and extragalactic gamma-ray background
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The abundance of primordial black holes from the global 21cm signal and extragalactic gamma-ray background Yupeng Yang1,2,a 1 School of Physics and Physical Engineering, Qufu Normal University, Qufu 273165, Shandong, China 2 Joint Center for Particle, Nuclear Physics and Cosmology, Nanjing 210093, Jiangsu, China
Received: 20 May 2020 / Accepted: 24 August 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Primordial black holes (PBHs) formed in the early Universe can accret dark matter particles due to gravity and form ultracompact minihalos (UCMHs). The theoretical researches and simulations have shown that the density profile of dark matter in UCMHs is in the form of ρ(r ) ∼ r −2.25 . Compared with the popular dark matter halo model, e.g., NFW model, dark matter annihilation rate is larger in UCMHs. Considering dark matter annihilation, there is a maximum core density ρmax in UCMHs which has been treated independent on redshift. While in this work, we point out that ρmax depends on redshift and dark matter annihilation rate in UCMHs also changes with time. We re-investigate the γ -ray flux from UCMHs due to dark matter annihilation and focus on their contributions to the extragalactic gamma-ray background (EGB). Utilizing the EGB data of Fermi, the constraints on the abundance of PBHs are derived, ΩPBH,EGB 2 × 10−8 . Motivated by the recent observations of global 21cm signals by the EDGES experiment, we investigate the influences of dark matter annihilation in UCMHs on global 21cm signals and derive the constraints on the abundance of PBHs, ΩPBH,21cm 2 × 10−10 . The derived constraints are valid for mass range of 10−6 M MPBH 103 M . 1 Introduction Primordial black holes (PBHs), formed through the collapse of large density perturbations in the early Universe can accrete dark matter particles by gravity and gradually develop ultracompact minihalos (UCMHs), dressed PBHs. The density profile of dark matter in UCMHs is in the form of ρ(r ) ∼ r −2.25 , which have been proved by theoretical researches and simulations [1–6]. Dark matter particles can annihilate into standard model particles shown by Weakly Interacting Massive Particles model [7,8], a popular researched dark matter model. It is expected that the annihilation rate of dark matter particles in UCMHs is larger than that of the classical dark matter halo model, e.g., NFW model. Therefore, UCMHs should have significant influences on the astrophysical observations and we will focus on the global 21cm signals and the extragalactic gamma-ray background (EGB). Dark matter annihilation in UCMHs contributes to the EGB, which has been investigated by, e.g., Refs. [4,5], and the constraints on the abundance of PBHs are obtained. The basic idea of these works is that the contributions of dark matter annihilation in UCMHs to the
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Eur. Phys. J. Plus
(2020) 135:690
EGB are similar to the case of dark matter
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