Bianchi type I cosmological models in Eddington-inspired Born-Infeld gravity

TL;DR

This paper explores the dynamics of anisotropic Bianchi type I cosmological models within Eddington-inspired Born-Infeld gravity, analyzing how different matter equations of state influence isotropization and evolution.

Contribution

It provides exact solutions and detailed analysis of anisotropic cosmologies in EiBI gravity, highlighting the role of initial conditions and matter types in cosmic evolution.

Findings

Dust-filled universes isotropize over time.

High-density matter universes' isotropization depends on initial energy density.

The models' evolution is governed by a nonlinear differential equation.

Abstract

We consider the dynamics of a barotropic cosmological fluid in an anisotropic, Bianchi type I space-time in Eddington-inspired Born-Infeld (EiBI) gravity. By assuming an isotropic pressure distribution, we obtain the general solution of the field equations in an exact parametric form. The behavior of the geometric and thermodynamic parameters of the Bianchi type I Universe is studied, by using both analytical and numerical methods, for some classes of high density matter, described by the stiff causal, radiation, and pressureless fluid equations of state. In all cases the study of the models with different equations of state can be reduced to the integration of a highly nonlinear second order ordinary differential equation for the energy density. The time evolution of the anisotropic Bianchi type I Universe strongly depends on the initial values of the energy density and of the Hubble function. An important observational parameter, the mean anisotropy parameter is also studied in detail, and we show that for the dust filled Universe the cosmological evolution always ends into an isotropic phase, while for high density matter filled universes the isotropization of Bianchi type I universes is essentially determined by the initial conditions of the energy density.