Primordial black holes from temporally enhanced curvature perturbation

TL;DR

This paper proposes a mechanism where a scalar field with generalized kinetic interactions causes a temporary boost in curvature perturbations, leading to primordial black hole formation and potential implications for early universe evolution and gravitational wave signals.

Contribution

It introduces a novel scenario where scalar fields induce temporal curvature perturbation enhancement, resulting in primordial black holes that influence the universe's expansion and observable tensor modes.

Findings

Primordial black holes can form efficiently during the enhanced curvature perturbation phase.

Black hole evaporation can reheat the universe, affecting its expansion history.

The model predicts distinctive primordial tensor mode signatures in the DECIGO frequency band.

Abstract

Scalar field with generalized kinetic interactions metamorphoses depending on its field value, ranging from cosmological constant to stiff matter. We show that such a scalar field can give rise to temporal enhancement of the curvature perturbation in the primordial Universe, leading to efficient production of primordial black holes while the enhancement persists. If the inflation energy scale is high, those mini-black holes evaporate by the Hawking radiation much before Big Bang nucleosynthesis and the effective reheating of the Universe is achieved by the black hole evaporation. Dominance of PBHs and the reheating by their evaporation modify the expansion history of the primordial Universe. This results in a characteristic feature of the spectrum of primordial tensor modes in the DECIGO frequency band, opening an interesting possibility of testing PBH reheating scenario by measuring the primordial tensor modes. If the inflation energy scale is low, the PBH mass can be much larger than the solar mass. In this case, PBH is an interesting candidate for seeds for supermassive black holes residing in present galaxies.