Phase Space Analysis of the Accelerating Multi-fluid Universe

TL;DR

This paper analyzes the phase space of a multi-fluid universe with various interactions, revealing fixed points and stability properties that shed light on early and late-time cosmic acceleration.

Contribution

It introduces a detailed phase space analysis of interacting cosmological fluids, including oscillating dark energy-dark matter interactions and their impact on universe evolution.

Findings

Identification of fixed points with physical significance

Demonstration of an oscillating interaction between dark energy and dark matter

Unification of early and late-time acceleration scenarios

Abstract

We study in detail the phase space of a Friedmann-Robertson-Walker Universe filled with various cosmological fluids which may or may not interact. We use various expressions for the equation of state, and we analyze the physical significance of the resulting fixed points. In addition we discuss the effects of the stability or an instability of some fixed points. Moreover we study an interesting phenomenological scenario for which there is an oscillating interaction between the dark energy and dark matter fluid. As we demonstrate, in the context of the model we use, at early times the interaction is negligible and it starts to grow as the cosmic time approaches the late-time era. Also the cosmological dynamical system is split into two distinct dynamical systems which have two distinct de Sitter fixed points, with the early-time de Sitter point being unstable. This framework gives an explicit example of the unification of the early-time with late-time acceleration. Finally, we discuss in some detail the physical interpretation of the various models we present in this work.