Kantowski-Sachs Einstein-Aether Scalar Field Cosmological Models: The Sequel

TL;DR

This paper explores how coupling between shear and scalar fields in Einstein-aether cosmology affects the universe's expansion, revealing anisotropic inflationary attractors and stable periodic orbits.

Contribution

It introduces a non-trivial shear-scalar coupling into Einstein-aether models and analyzes its impact on stability and asymptotic behavior of cosmological solutions.

Findings

Anisotropic power-law inflationary attractors are stabilized by shear coupling.

Stable periodic orbits exist for specific parameter ranges with shear-scalar coupling.

Coupling influences the stability and nature of equilibrium points in the model.

Abstract

Utilizing the autonomous system of ordinary differential equations derived in arXiv:1809.01458 to define the evolution, we further investigate a class of cosmological models within an Einstein-aether gravitational framework by introducing a non-trivial coupling between the shear of the aether field to the scalar field on the future asymptotic solution. We subsequently conduct qualitative and numerical stability analysis on the new set of equilibrium points and paramountly determine that the expansionary power-law inflationary attractor becomes anisotropic rather than isotropic in the presence of such a coupling. It is further shown that the stability of this solution is dependent on the value of the shear coupling parameter $a3$. We also discover a family of asymptotically stable periodic orbits which exist for a particular range of parameter values within the Bianchi I invariant set and vanish in the absence of coupling between the aether field and the scalar field.