Anisotropic Spacetimes in $f(G)$-gravity: Bianchi I, Bianchi III and Kantowski-Sachs Cosmologies

TL;DR

This paper explores the evolution of anisotropic cosmological models in $f(G)$-gravity, revealing attractors like Minkowski space and isotropic accelerated expansion, while also identifying instabilities and singularities.

Contribution

It reformulates $f(G)$-gravity with a Lagrange multiplier, linking it to scalar field models, and analyzes anisotropic cosmologies numerically to identify key dynamical attractors.

Findings

Existence of Minkowski and isotropic accelerated expansion attractors.

De Sitter expansion is unstable in this framework.

Presence of Big Rip singularities.

Abstract

We investigate the evolution of cosmological anisotropies within the framework of $f\left(G\right)$-gravity. Specifically, we consider a locally rotationally symmetric geometry in four-dimensional spacetime that describes the Bianchi I, Bianchi III, and the Kantowski-Sachs spacetimes. Within this context, we introduce a Lagrange multiplier which allows us to reformulate the geometric degrees of freedom in terms of a scalar field. The resulting theory is dynamically equivalent to an Einstein-Gauss-Bonnet scalar field model. We normalize the field equations by introducing dimensionless variables. The dynamics of our system is then explored by solving the resulting nonlinear differential equations numerically for various sets of initial conditions. Our analysis reveals the existence of two finite attractors: the Minkowski universe and an isotropic, spatially flat solution capable of describing accelerated expansion. Although de Sitter expansion may be recovered, it appears only as an unstable solution. In addition, the theory suffers from the existence of Big Rip singularities.