Exact Global Solutions of Brane Universes and Big Bounce

TL;DR

This paper derives exact solutions for five-dimensional brane universe models, revealing a big bounce scenario instead of a big bang and analyzing how energy density depends on the fifth dimension's size.

Contribution

It provides the first exact global solutions for 5D brane cosmologies with a $S_1/Z_2$ orbifold, showing a universe starting from a big bounce rather than a big bang.

Findings

Universe begins from a big bounce, not a big bang.

Before the bounce, the universe was in a contracting phase.

Energy density on the second brane varies with the fifth dimension's size.

Abstract

Exact global solutions of five-dimensional cosmological models compactified on a $S_1/Z_2$ orbifold with two 3-branes are presented, and evolution of a simple model is studied. It is found that on all 4D spacetime hypersurfaces, except a singular one, the expanding universe was started not from a big bang but from a big bounce, and before the bounce the universe was in a deflationary contracting phase. It is also found that whether the energy density on the second brane is positive, zero, or negative depends on the size of the fifth dimension.