Dynamics of the universe with disformal coupling between the dark sectors

TL;DR

This paper investigates the late-time evolution of the universe considering a disformal coupling between dark energy and dark matter, revealing new classes of stable fixed points influenced by the disformal coefficient's dependence on scalar field and kinetic terms.

Contribution

It extends previous models by allowing the disformal coefficient to depend on both the scalar field and its kinetic terms, identifying new classes of fixed points and their stability conditions.

Findings

Two classes of scaling fixed points can describe late-time acceleration.

Stable fixed points can have different values for the same parameters, depending on initial conditions.

Dependence on kinetic terms introduces saddle points and affects stability.

Abstract

We use the dynamical analysis to study the evolution of the universe at late time for the model in which the interaction between dark energy and dark matter is inspired by disformal transformation. We extend the analysis in the existing literature by supposing that the disformal coefficient depends both on the scalar field and its kinetic terms. We find that the dependence of the disformal coefficient on the kinetic term of scalar field leads to two classes of the scaling fixed points that can describe the acceleration of the universe at late time. The first class exists only for the case where the disformal coefficient depends on the kinetic terms. The fixed points in this class are saddle points unless the slope of the conformal coefficient is sufficiently large. The second class can be viewed as the generalization of the fixed points studied in the literature. According to the stability analysis of these fixed points, we find that the stable fixed point can take two different physically relevant values for the same value of the parameters of the model. These different values of the fixed points can be reached for different initial conditions for the equation of state parameter of dark energy. We also discuss the situations in which this feature disappears.