Isocurvature Constraints on Dark Matter from Evaporated Primordial Black Holes

TL;DR

This paper examines how isocurvature perturbations from primordial black hole evaporation can constrain dark matter models, considering non-Gaussianity effects and multiple production mechanisms.

Contribution

It provides a detailed analysis of isocurvature perturbations in PBH evaporation scenarios and reassesses constraints from dark matter overproduction and gravitational waves.

Findings

Isocurvature perturbations can significantly constrain dark matter from PBH evaporation.

Non-Gaussianity enhances isocurvature effects on cosmological scales.

Multiple production mechanisms influence dark matter abundance and related constraints.

Abstract

We revisit the scenario in which stable particles of a dark sector are produced through the complete evaporation of light primordial black holes (PBHs) formed in the early Universe. We investigate in detail the role of isocurvature perturbations that may arise in this framework. PBHs inherit Poisson fluctuations on unobservable small scales at formation; however, in the presence of primordial non-Gaussianity that couples long- and short-wavelength modes, these fluctuations can source isocurvature perturbations on cosmological scales. Such perturbations are unavoidably transferred to the dark sector particles emitted via Hawking evaporation. We highlight the potential impact of isocurvature constraints on dark sector particles produced through PBH evaporation. Along the way, we re-assess the constraints on this scenario arising from the overproduction of dark matter (DM), accounting for both PBH evaporation and gravitational production (freeze-in) during (after) inflation, as well as bounds from warm DM and the overproduction of scalar-induced gravitational waves.