CMB constraints on ultra-light primordial black holes with extended mass distributions

Abstract

We examine the effects ultra-light primordial black holes (PBHs) have on the anisotropies of the cosmic microwave background (CMB). PBHs in the mass range of $10^{15}$ to $10^{17}$ g emit Hawking radiation in the early Universe, modifying the standard recombination history. This leads to a damping of small-scale temperature and polarisation anisotropies and enhances large-scale polarisation fluctuations. As some models of inflation predict PBHs with a range of masses, we investigate the impacts of extended mass distributions on PBH abundance constraints. We model PBH energy injection using a ground-up approach incorporating species-dependent deposition efficiencies. By allowing the $\Lambda$CDM parameters to vary simultaneously with the PBH fraction and mass, we show that exclusion bounds on the PBH fraction of DM $f_{\text{PBH}}$ are relaxed by up to an order of magnitude, compared to the case of fixed $\Lambda$CDM parameters. We also give 95% exclusion regions for $f_{\text{PBH}}$ for a variety of mass distributions. In particular, for a uniform mass distribution between $10^{15}$ and $10^{17}$ g, we find $f_{\text{PBH}}<1.6\times 10^{-5}$ when allowing $\Lambda$CDM parameters to vary.

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• Primordial Black Holes as Dark Matter
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• CMB bounds on disk-accreting massive Primordial Black Holes
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Cited by in corpus (1)

• Constraining primordial black holes as dark matter using the global 21-cm signal with X-ray heating and excess radio background