Fitting power spectrum of scalar perturbations for primordial black hole production during inflation

TL;DR

This paper introduces an analytic fit for the scalar power spectrum during inflation, combining slow-roll and peak enhancement components, to better understand primordial black hole formation and dark matter composition.

Contribution

It presents a novel analytic model for the power spectrum that incorporates both slow-roll and peak features, aiding primordial black hole formation studies.

Findings

The fit aligns with CMB observations from Planck/BICEP/Keck.

Restrictions on peak width and parameters for PBH dark matter are derived.

The model supports primordial black holes as dark matter candidates.

Abstract

We propose a simple analytic fit for the power spectrum of scalar (curvature) perturbations during inflation, in order to describe slow roll of inflaton and formation of primordial black holes in the early universe, in the framework of single-field models. Our fit is given by a sum of the power spectrum in the slow-roll approximation, needed for a viable description of the cosmic microwave background radiation in agreement with Planck/BICEP/Keck measurements, and the log-normal (Gaussian) fit for the power spectrum enhancement (peak) needed for efficient production of primordial black holes. We use the T-type $\alpha$-attractor models in order to describe slow-roll inflation. Demanding the location and height of the peak to yield the masses of primordial black holes in the asteroid-size window allowed for the whole (current) dark matter to be composed of the primordial black holes, we find the restrictions on the remaining parameters and, most notably, on the width of the peak.