paper

Anisotropic Spacetimes in -gravity: Bianchi I, Bianchi III and Kantowski-Sachs Cosmologies

arXiv:2508.18055 · doi:10.1007/s10714-025-03465-3

Abstract

We investigate the evolution of cosmological anisotropies within the framework of -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.

arXiv comment15 pages, 8 Figures, to appear in Gen. Rel. Grav

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