Cosmological implications of Primordial Black Holes

TL;DR

This paper examines how primordial black holes as dark matter candidates influence cosmological parameters and constraints using cosmic microwave background data, highlighting degeneracies and the importance of polarization measurements.

Contribution

It provides the first detailed analysis of cosmological implications of PBHs, including degeneracies with standard parameters and constraints on extended mass distributions from CMB data.

Findings

Significant degeneracies between PBHs and cosmological parameters.

Small scale polarization data reduces degeneracies.

Extended mass distributions yield tighter constraints.

Abstract

The possibility that a relevant fraction of the dark matter might be comprised of Primordial Black Holes (PBHs) has been seriously reconsidered after LIGO's detection of a $\sim 30 M_{\odot}$ binary black holes merger. Despite the strong interest in the model, there is a lack of studies on possible cosmological implications and effects on cosmological parameters inference. We investigate correlations with the other standard cosmological parameters using cosmic microwave background observations, finding significant degeneracies, especially with the tilt of the primordial power spectrum and the sound horizon at radiation drag. However, these degeneracies can be greatly reduced with the inclusion of small scale polarization data. We also explore if PBHs as dark matter in simple extensions of the standard $\Lambda$CDM cosmological model induces extra degeneracies, especially between the additional parameters and the PBH's ones. Finally, we present cosmic microwave background constraints on the fraction of dark matter in PBHs, not only for monochromatic PBH mass distributions but also for popular extended mass distributions. Our results show that extended mass distribution's constraints are tighter, but also that a considerable amount of constraining power comes from the high-$\ell$ polarization data. Moreover, we constrain the shape of such mass distributions in terms of the correspondent constraints on the PBH mass fraction.