CMB and 21cm bounds on early structure formation boosted by primordial black hole entropy fluctuations

Abstract

The dark matter (DM) can consist of the primordial black holes (PBHs) in addition to the conventional weakly interacting massive particles (WIMPs). The Poisson fluctuations of the PBH number density produce the isocurvature perturbations which can dominate the matter power spectrum at small scales and enhance the early structure formation. We study how the WIMP annihilation from those early formed structures can affect the CMB (in particular the E-mode polarization anisotropies and $y$-type spectral distortions) and global 21cm signals. Our studies would be of particular interest for the light (sub-GeV) WIMP scenarios which have been less explored compared with the mixed DM scenarios consisting of PBHs and heavy ($\gtrsim 1$ GeV) WIMPs. For instance, for the self-annihilating DM mass $m_{\chi }=1$ MeV and the thermally averaged annihilation cross section $⟨\sigma v⟩\sim 10^{-30}\mathrm{c}{\mathrm{m}}^3/s$, the latest Planck CMB data requires the PBH fraction with respect to the whole DM to be at most $\mathcal{O}(10^{-3})$ for the sub-solar mass PBHs and an even tighter bound (by a factor $\sim 5$) can be obtained from the global 21-cm measurements.

14 pages, 10 figures

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Cited by in corpus (7)

• Accelerating early massive galaxy formation with primordial black holes
• Constraining primordial black holes as dark matter using the global 21-cm signal with X-ray heating and excess radio background
• Primordial Black Holes
• Primordial Black Hole Dark Matter in the Context of Extra Dimensions
• Primordial black hole dark matter in the presence of p-wave WIMP annihilation
• Radio bounds on the mixed dark matter scenarios of primordial black holes and WIMPs
• Probing isocurvature perturbations with 21-cm global signal in the light of HERA result