Primordial Black Holes from $\alpha$-attractors

TL;DR

This paper explores how $ ext{alpha}$-attractor inflation models can produce primordial black holes with specific masses and abundances, linking the curvature power spectrum features to postinflationary cosmic evolution and CMB observables.

Contribution

It demonstrates that $ ext{alpha}$-attractor models can generate primordial black holes with significant abundance through moderate tuning of the potential parameters.

Findings

Primordial black holes in the mass range $10^{-16}-10^{-14} M_{igodot}$ can form with relevant abundance.

A power spectrum peak of ${ m P_R} o 10^{-2}$ leads to significant PBH formation.

CMB predictions include smaller $n_s$ and larger $r$, $ ext{alpha}_s$ compared to standard models.

Abstract

We consider primordial black hole (PBH) production in inflationary $\alpha$-attractors. We discuss two classes of models, namely models with a minimal polynomial superpotential as well as modulated chaotic ones that admit PBHs. We find that a significant amplification of the curvature power spectrum ${\cal P_R}$ can be realized in this class of models with a moderate tuning of the potential parameters. We consistently examine the PBH formation during radiation and additionally during reheating eras where the background pressure is negligible. It is shown that basic features of the curvature power spectrum are explicitly related with the postinflationary cosmic evolution and that the PBH mass and abundance expressions are accordingly modified. PBHs in the mass range $10^{-16}-10^{-14} \, M_{\odot}$ can form with a cosmologically relevant abundance for a power spectrum peak ${\cal P_R} \sim 10^{-2}$ and large reheating temperature and, furthermore, for a moderate peak ${\cal P_R} \sim 10^{-5}$ and reheating temperature $T_\text{rh}\sim 10^7$ GeV, characteristic of the position of the power spectrum peak. Regarding the CMB observables, the $\alpha$-attractor models utilized here to generate PBH in the low-mass region predict in general a smaller $n_s$ and larger $r$ and $\alpha_s$ parameter values compared to the conventional inflationary $\alpha$-attractor models.