Big bang of the brane universe

TL;DR

This paper investigates the initial singularity of the FRW-brane universe, revealing it is point-like causally and identifying null singularities in flat and open models, contrasting with traditional big bang models.

Contribution

It introduces a causal perspective on the initial singularity in brane cosmology and identifies null singularities in specific FRW-brane models.

Findings

Initial singularity is point-like causally in brane universe.

Null singularities are present in flat and open models.

Contrasts with the spacelike singularity of standard FRW universe.

Abstract

Big bang of the Friedmann-Robertson-Walker (FRW)-brane universe is studied. In contrast to the spacelike initial singularity of the usual FRW universe, the initial singularity of the FRW-brane universe is point-like from the viewpoint of causality including gravitational waves propagating in the bulk. Existence of null singularities (seam singuralities) is also shown in the flat and open FRW-brane universe models.