Exactly solved models of interacting dark matter and dark energy

TL;DR

This paper develops an effective one-fluid model for the interacting dark sector in cosmology, analyzing stability, solutions, and specific interaction forms that can address the coincidence problem and produce various cosmological scenarios.

Contribution

It introduces a unified framework for modeling dark matter and dark energy interactions, including nonlinear interactions, and explores their implications for cosmological evolution.

Findings

Derived the source equation for total energy density.

Identified conditions for stability of solutions.

Found that nonlinear interactions can produce relaxed Chaplygin gas models.

Abstract

We introduce an effective one-fluid description of the interacting dark sector in a spatially flat Friedmann-Robertson-Walker space-time and investigate the stability of the power-law solutions. We find the "source equation" for the total energy density and determine the energy density of each dark component. We study linear and nonlinear interactions which depend on the dark matter and dark energy densities, their first derivatives, the total energy density with its derivatives up to second order and the scale factor. We solve the evolution equations of the dark components for both interactions, examine exhaustively several examples and show cases where the problem of the coincidence is alleviated. We show that a generic nonlinear interaction gives rise to the "relaxed Chaplygin gas model" whose effective equation of state includes the variable modified Chaplygin gas model while some others nonlinear interactions yield de Sitter and power-law scenarios.