A Faster Growth of Perturbations in an Early Matter Dominated Epoch: Primordial Black Holes and Gravitational Waves

TL;DR

This paper proposes a scenario where rapid growth of early universe perturbations leads to primordial black hole formation and gravitational wave production, with implications for dark matter and cosmology.

Contribution

It introduces a model with fast perturbation growth during an early matter era influenced by a dark fermion and scalar force, linking to PBH and GW phenomenology.

Findings

Primordial black holes in sub-lunar mass range can form.

Gravitational waves produced across a wide frequency spectrum.

Fast perturbation growth with s > 10 during early matter domination.

Abstract

We present a scenario for fast growth of cosmological perturbations; $\delta(t) \sim a(t)^s$, $a(t)$ being the scale factor, with $s > 10$ for the numerical examples reported in this article. The basic ingredients of the scenario are an early matter dominated era and the dark fermion which experiences a scalar mediated force during the epoch. Both of these arise in string/supergravity models. The fast growth occurs for sub-horizon density perturbations of the dark fermion. The fast growth has a rich set of phenomenological implications. We outline implications for the formation of primordial black holes and the production of gravitational waves. Primordial black holes in the sub-lunar mass range (which are ideal dark matter candidates) can be produced. Gravitational waves can be produced in a wide range of frequencies due to second order scalar perturbations and due to evaporation and merger of primordial black holes.