Interacting Kasner-type cosmologies

TL;DR

This paper explores multi-fluid Kasner-type cosmologies, analyzing anisotropic expansion with interacting and non-interacting fluids, revealing the existence of scaling solutions and energy transfer mechanisms, with some matter components violating energy conditions.

Contribution

It introduces a comprehensive study of relativistic multi-fluid Kasner cosmologies, including interactions and energy transfer, expanding understanding of anisotropic universe models.

Findings

Existence of cosmological scaling solutions for two-fluid scenarios.

More general solutions appear in three-fluid configurations.

Energy transfer among fluids can violate energy conditions.

Abstract

It is well known that Kasner-type cosmologies provide a useful framework for analyzing the three-dimensional anisotropic expansion because of the simplification of the anisotropic dynamics. In this paper relativistic multi-fluid Kasner-type scenarios are studied. We first consider the general case of a superposition of two ideal cosmic fluids, as well as the particular cases of non-interacting and interacting ones, by introducing a phenomenological coupling function $q(t)$. For two-fluid cosmological scenarios there exist only cosmological scaling solutions, while for three-fluid configurations there exist not only cosmological scaling ones, but also more general solutions. In the case of triply interacting cosmic fluids we can have energy transfer from two fluids to a third one, or energy transfer from one cosmic fluid to the other two. It is shown that by requiring the positivity of energy densities there always is a matter component which violates the dominant energy condition in this kind of anisotropic cosmological scenarios.