Bouncing Cosmologies

TL;DR

This paper reviews nonsingular and cyclic cosmologies, focusing on bounce mechanisms, solution examples, and their observational implications, especially regarding perturbation behavior in regular universes.

Contribution

It provides a comprehensive overview of bounce mechanisms and analyzes specific solutions and their observational consequences in nonsingular cosmological models.

Findings

Identification of key bounce mechanisms

Examples of solutions implementing bounce

Implications for perturbation behavior and observations

Abstract

We review the general features of nonsingular universes ({\em i.e.} those that go from an era of accelerated collapse to an expanding era without displaying a singularity) as well as cyclic universes. We discuss the mechanisms behind the bounce, and analyze examples of solutions that implement these mechanisms. Observational consequences of such regular cosmologies are also considered, with emphasis in the behavior of the perturbations.