Axionic extension of the Einstein-aether theory: How does dynamic aether regulate the state of axionic dark matter?

TL;DR

This paper introduces a model where the dynamic aether influences axionic dark matter through a modified Higgs potential, resulting in a stiff equation of state and stable cosmological behavior.

Contribution

It presents a novel axionic extension of Einstein-aether theory with a dynamic potential dependent on the aether's covariant derivative, providing exact solutions in cosmology.

Findings

Effective stiff equation of state for axionic dark matter.

Homogeneous perturbations decay over time, indicating stability.

Exact solutions in homogeneous isotropic cosmology.

Abstract

In the framework of axionic extension of the Einstein-aether theory we establish the model, which describes a stiff regulation of the behavior of axionic dark matter by the dynamic aether. The aether realizes this procedure via the modified Higgs potential, designed for modeling of nonlinear self-interaction of pseudoscalar (axion) field; the modification of this potential is that its minima are not fixed, and their positions and depths depend now on the square of the covariant derivative of the aether velocity four-vector. Exact solutions to the master equations, modified correspondingly, are obtained in the framework of homogeneous isotropic cosmological model. The effective equation of state for axionic dark matter is of the stiff type. Homogeneous perturbations of the pseudoscalar (axion) field, of the Hubble function and of the scale factor are shown to fade out with cosmological time, there are no growing modes, the model of stiff regulation is stable.