Cosmological Constraints from Primordial Black Holes

TL;DR

This paper reviews how primordial black holes, formed in the early universe, impose constraints on cosmological models, especially on the spectral index of density perturbations, considering their evolution from formation to present.

Contribution

It analyzes the dependence of primordial black hole constraints on the full cosmological history and highlights their significance in constraining the spectral index of density perturbations.

Findings

Black holes provide strong constraints on the spectral index n.

Constraints depend on the cosmological history model.

Current constraints are based on black hole evaporation and observational limits.

Abstract

Primordial black holes may form in the early Universe, for example from the collapse of large amplitude density perturbations predicted in some inflationary models. Light black holes undergo Hawking evaporation, the energy injection from which is constrained both at the epoch of nucleosynthesis and at the present. The failure as yet to unambiguously detect primordial black holes places important constraints. In this article, we are particularly concerned with the dependence of these constraints on the model for the complete cosmological history, from the time of formation to the present. Black holes presently give the strongest constraint on the spectral index $n$ of density perturbations, though this constraint does require $n$ to be constant over a very wide range of scales.