Dynamics of expansion of the Universe in model with the additional coupling between dark energy and dark matter

TL;DR

This paper investigates the evolution of the Universe's expansion in a model with nonminimally coupled dark energy and dark matter, analyzing different interaction types and deriving conditions for positive energy densities.

Contribution

It introduces a detailed analysis of interacting dark energy and dark matter with variable EoS and provides analytical and numerical solutions for their density evolution.

Findings

Analytical expressions for densities with proportional sum interaction.

Numerical analysis of densities with proportional product interaction.

Constraints on interaction parameters to keep densities positive.

Abstract

We study the dynamics of expansion of the homogeneous isotropic Universe and the evolution of its components in the model with nonminimally coupled dynamical dark energy. Dark energy, like the other components of the Universe, is described by the perfect fluid approximation with the equation of state (EoS) $p_ {de}=w\rho_{de}$, where the EoS parameter $w$ depends on time and is parameterized via the squared adiabatic sound speed $c_{ a}^2$ which is assumed to be constant. On basis of the general covariant conservation equations for the interacting dark energy and dark matter and Einstein equations in Friedmann-Lemaitre-Robertson-Walker metric we analyze the evolution of energy densities of the hidden components and the dynamics of expansion of the Universe with two types of interaction: proportional to the sum of densities of the hidden components and proportional to their product. For the first interaction the analytical expressions for the densities of dark energy and dark matter were obtained and analyzed in detail. For the second one the evolution of densities of hidden components of the Universe was analyzed on basis of the numerical solutions of their energy-momentum conservation equations. For certain values of the parameters of these models the energy densities of dark components become negative. So to ensure that the densities are always positive we put constraints on the interaction parameter for both models.