Bouncing Braneworlds

TL;DR

This paper explores cosmological models with a timelike extra dimension, revealing that such models can naturally avoid singularities through a bounce, leading to non-singular or quasi-singular origins of the universe.

Contribution

It demonstrates that timelike extra dimensions in braneworld models can prevent singularities and produce non-singular or quasi-singular cosmological origins, extending previous models with spacelike dimensions.

Findings

Contracting braneworlds can bounce without singularity.

Timelike extra dimensions lead to non-singular or quasi-singular origins.

Distinct behavior from models with spacelike extra dimensions.

Abstract

We study cosmological braneworld models with a single timelike extra dimension. Such models admit the intriguing possibility that a contracting braneworld experiences a natural bounce without ever reaching a singular state. This feature persists in the case of anisotropic braneworlds under some additional and not very restrictive assumptions. Generalizing our study to braneworld models containing an induced brane curvature term, we find that a FRW-type singularity is once again absent if the bulk extra dimension is timelike. In this case, the universe either has a non-singular origin or commences its expansion from a quasi-singular state during which both the Hubble parameter and the energy density and pressure remain finite while the curvature tensor diverges. The non-singular and quasi-singular behaviour which we have discovered differs both qualitatively and quantitatively from what is usually observed in braneworld models with spacelike extra dimensions and could have interesting cosmological implications.