Gauss-Bonnet brane-world cosmology without Z2-symmetry

We consider a single 3-brane situated between two bulk spacetimes that possess the same cosmological constant, but whose metrics do not possess a Z2-symmetry. On each side of the brane, the bulk is a solution to Gauss-Bonnet gravity. This asymmetry modifies junction conditions, so new terms arise in the Friedmann equation. If Z2-breaking terms become dominant, they behave as a cosmological constant at early times for one case and might remove the initial singularity for the other case. However, we show that these new terms cannot become the dominant ones under the usual conditions when our brane is outside an event horizon. We also show that any brane-world scenarios of this type revert to a Z2-symmetric form at late times, and hence rule out certain proposed scenarios