Evolution of Anisotropies in Eddington-Born-Infeld Cosmology

TL;DR

This paper investigates the evolution of anisotropies in Eddington-Born-Infeld cosmology, demonstrating that residual anisotropies decay over time with a damped oscillatory pattern, potentially avoiding standard bounds through initial condition tuning.

Contribution

It extends the Eddington-Born-Infeld model to Bianchi type I cosmology and analyzes anisotropy decay, revealing a damped oscillatory behavior distinct from standard exponential decay.

Findings

Residual anisotropies decay over time in the model.

Shears decay with a damped oscillatory pattern.

Standard bounds on anisotropies can be avoided with initial condition tuning.

Abstract

Recently a Born-Infeld action for dark energy and dark matter that uses additional affine connections was proposed. At background level, it was shown that the new proposal can mimic the standard cosmological evolution. In Bianchi cosmologies, contrary to the scalar field approach (e.g., Chaplygin gas), the new approach leads to anisotropic pressure, raising the issues of stability of the isotropic solution under anisotropic perturbations and, being it stable, how the anisotropies evolve. In this work, the Eddington-Born-Infeld proposal is extended to a Bianchi type I scenario and residual post-inflationary anisotropies are shown to decay in time. Moreover, it is shown that the shears decay following a damped oscillatory pattern, instead of the standard exponential-like decay. Allowing for some fine tuning on the initial conditions, standard theoretical bounds on the shears can be avoided.