Cosmological Bounce Relics: Black Holes, Gravitational Waves, and Dark Matter

TL;DR

This paper introduces a novel mechanism in bouncing cosmology that produces relic black holes, gravitational waves, and dark matter through collapse processes before and after the bounce, offering a unified origin for these phenomena.

Contribution

It presents a new model for relic formation in bouncing universes, distinct from inflationary scenarios, with detailed conditions for horizon crossing and survival of structures.

Findings

Relics can survive the bounce if larger than 90 m.

Relic black holes and GWs cover a wide mass range.

Provides a unified origin for dark matter and gravitational waves.

Abstract

We propose a new mechanism for generating cosmological relics -- black holes, gravitational waves (GWs), and possibly dark matter (DM) -- in a bouncing Universe. Relics arise through two channels: (i) compact objects and GWs produced during pre-bounce collapse that remain super-horizon and re-enter after the bounce, and (ii) dark-matter halos formed during collapse that exit the horizon and collapse into black holes upon re-entry. Unlike inflationary primordial black holes, these relic black holes originate from nonlinear structure formation during collapse. We derive the particle horizon and horizon-crossing conditions in bouncing cosmology and show that perturbations or compact objects larger than 90 m survive the bounce. The resulting population of relic black holes and GWs spans a wide mass range, offering a unified origin for dark matter, gravitational-wave backgrounds, and the early growth of supermassive black holes and galaxies.