Formation of Primordial Black Holes from Warm Inflation

TL;DR

This paper investigates how warm inflation models can produce primordial black holes with specific mass ranges, analyzing their formation, abundance, and potential role as dark matter relics, consistent with cosmic microwave background observations.

Contribution

It introduces a warm inflation model that naturally generates a primordial power spectrum with features conducive to PBH formation, including a red tilt at large scales and a blue tilt at small scales.

Findings

PBHs with mass ~10^3 g can form with significant abundance.

The model's power spectrum matches CMB constraints at large scales.

Tiny PBHs would have evaporated early, leaving potential relics.

Abstract

Primordial Black Holes (PBHs) serve as a unique probe to the physics of the early Universe, particularly inflation. In light of this, we study the formation of PBHs by the collapse of overdense perturbations generated during a model of warm inflation. For our model, we find that the primordial curvature power spectrum is red-tilted (spectral index $n_s<1$) at the large scale (small $k$) and is consistent with the $n_s-r$ values allowed from the CMB observations. Along with that, it has a blue-tilt ($n_s>1$) for the small PBH scales (large $k$), with a sufficiently large amplitude of the primordial curvature power spectrum required to form PBHs. These features originate because of the inflaton's coupling with the other fields during warm inflation. We discuss the role of the inflaton dissipation to the enhancement in the primordial power spectrum at the PBH scales. We find that for some parameter range of our warm inflation model, PBHs with mass $\sim 10^3$ g can be formed with significant abundance. Such tiny mass PBHs have a short lifetime $\sim 10^{-19}$ s and would have evaporated into Hawking radiation in the early Universe. Further in this study, we discuss the evaporation constraints on the initial mass fraction of the generated PBHs and the possibility of Planck mass PBH relics to constitute the dark matter.