# Splitting into two isotropic subspaces as a result of cosmological evolution in Einstein-Gauss-Bonnet gravity

## TL;DR

This paper studies the evolution of a flat anisotropic universe in Einstein-Gauss-Bonnet gravity, showing that cosmological evolution often results in a split into two isotropic subspaces, with outcomes including singular, oscillatory, or exponential solutions.

## Contribution

It demonstrates that in Einstein-Gauss-Bonnet cosmology, the universe can naturally evolve into a split into two isotropic subspaces, a phenomenon previously not well understood.

## Key findings

- Three possible evolution outcomes: singular, oscillatory, exponential.
- Evolution often leads to a split into two isotropic subspaces.
- Such splitting occurs even when de Sitter solutions are present.

## Abstract

We consider numerically dynamics of a flat anisotropic Universe in Einstein-Gauss-Bonnet gravity with positive $\Lambda$ in dimensionalities 5+1 and 6+1. We identify three possible outcomes of the evolution, one singular and two nonsingular. First nonsingular outcome is oscillatory. Second is the known exponential solution. The simplest version of it is the isotropic de Sitter solution. In Gauss-Bonnet cosmology there exist also anisotropic exponential solutions. When an exponential solution being an outcome of cosmological evolution has two different Hubble parameters, the evolution leads from initially totally anisotropic stage to a sum of two isotropic subspaces. We show that such type of evolution is rather typical and possible even in the case when de Sitter solution also exists.