A study of interacting scalar field model from the perspective of the dynamical systems theory

TL;DR

This paper analyzes scalar field models as dark energy interacting with dark matter using dynamical systems theory, identifying critical points and stability conditions to understand late-time cosmic acceleration.

Contribution

It introduces two interaction models with different potentials and couplings, deriving autonomous systems and analyzing their critical points and stability in the context of cosmic evolution.

Findings

Scalar field dominated solutions for late-time acceleration.

Existence of scaling solutions alleviating the coincidence problem.

De Sitter-like solutions indicating transient universe evolution.

Abstract

In this work, considering the background dynamics of flat Friedmann-Lemaitre-Robertson-Walker(FLRW) model of the universe, we investigate a scalar field model as dark energy candidate which interacting with the pressure-less dust as dark matter from dynamical systems perspective. From phenomenological vantage point two interaction terms are chosen: one depends on Hubble parameter $H$ and other is local, independent of Hubble parameter. In interaction model 1, the scalar field potential as well as the coupling are considered to be in the form of inverse square and accordingly a two-dimensional autonomous system is obtained. On the other hand, Interaction model 2 comprises with the potential as well as coupling of scalar field which are considered in form of exponential function of scalar field ($\phi$) and as a result of which a four-dimensional autonomous system is achieved. We study two systems separately and come by several critical points in 2D system as well as in 4D system. We have derived sound speed and the classical stability conditions. Furthermore, for 2D autonomous system we analyzed the stability of some critical points at infinity. From this autonomous system, we obtain scalar field dominated solutions representing late time accelerated evolution of the universe that does not elucidate the coincidence problem. Late time scaling solutions are also realized by the accelerated expansion of the universe which evolves in quintessence era that alleviates the coincidence problem successfully. From the analysis of 4D system, we obtain non-hyperbolic sets of critical points which are analyzed by the center manifold theory. In this model, the de Sitter like solutions represent the transient evolution of the universe.