The effect of outflows on CMB bounds from Primordial Black Hole accretion

Abstract

Should Primordial Black Holes (PBHs) exist in nature, they would inevitably accrete baryonic matter in their vicinity. In turn, the consequent emission of high-energy radiation could affect the thermal history of the universe to an extent that can be probed with a number of cosmological observables such as the Cosmic Microwave Background (CMB) anisotropies. However, our understanding of the accretion and radiation emission processes in the context of PBHs is still in its infancy, and very large theoretical uncertainties affect the resulting constraints on the PBH abundance. Building on state-of-the-art literature, in this work we take a step towards the development of a more realistic picture of PBH accretion by accounting for the contribution of outflows. Specifically, we derive CMB-driven constraints on the PBH abundance for various accretion geometries, ionization models and mass distributions in absence and in presence of mechanical feedback and non-thermal emissions due to the outflows. As a result, we show that the presence of such outflows introduces an additional layer of uncertainty that needs to be taken into account when quoting cosmological constraints on the PBH abundance, with important consequences in particular in the LIGO-Virgo-KAGRA observational window.

Constraining extended cosmologies with GW×LSS cross-correlations

“…Even though the number of events detected by a second generation GW detector network at design sensitivity appear to be insufficient to establish the origin of the binary due to volume selection effects that smears out the relative differences between models, we find that third generation detectors will be able to either rule in or out PBHs as a major component of the dark matter at more than 3σ confidence level in the tens of solar masses range. Therefore GW clustering can be effectively used to robustly constraint the abundance of PBH in a mass range that is heavily probed [143][144][145][146][147][148][149][150][151][152][153][154][155][156][157][158][159][160], but still suffers from large theoretical uncertainties due to the theoretical modelling of the observables and the unknown PBH mass distribution, see, e.g., refs. [160,161].…”

“…Therefore GW clustering can be effectively used to robustly constraint the abundance of PBH in a mass range that is heavily probed [143][144][145][146][147][148][149][150][151][152][153][154][155][156][157][158][159][160], but still suffers from large theoretical uncertainties due to the theoretical modelling of the observables and the unknown PBH mass distribution, see, e.g., refs. [160,161]. Finally, we note that it is more difficult to probe PBH abundances of f PBH ≲ 0.1, independently on the relative abundance of late time and early time PBH binaries.…”