Cosmological dynamics of the general non-canonical scalar field models

Jibitesh Dutta,Hmar Zonunmawia,Wompherdeiki Khyllep

doi:10.1140/epjc/s10052-019-6885-2

Abstract

We extend the investigation of cosmological dynamics of the general non-canonical scalar field models by dynamical system techniques for a broad class of potentials and coupling functions. In other words, we do not restrict the analysis to exponential or power-law potentials and coupling functions. This type of investigation helps in understanding the general properties of a class of cosmological models. In order to better understand the phase space of the models, we investigate the various special cases and discuss the stability and viability issues. Performing a detailed stability analysis, we show that it is possible to describe the cosmic history of the universe at the background level namely the early radiation dominated era, intermediate matter dominated era and the late time dark energy domination. Moreover, we find that we can identify a broad class of potentials and coupling functions for which it is possible to get an appealing unified description of dark matter and dark energy. The results obtained here, therefore, enlarge the previous analyses wherein only a specific potential and coupling functions describe the unification of dark sectors. Further, we also observe that a specific scenario can also possibly explain the phenomenon of slow-roll inflationary exit.

Highlights

The most general non-canonical form of a scalar field which involves higher order derivatives of a scalar field falls under the well-known Horndeski Lagrangian [10]
A simple form of a non-canonical scalar field model is collectively known as k-essence, the first term of the Horndeski Lagrangian
The organisation of the paper is as follows: In Sect. 2, we briefly review the basic equations of the non-canonical scalar field models

Summary

Introduction

The most general non-canonical form of a scalar field which involves higher order derivatives of a scalar field falls under the well-known Horndeski Lagrangian [10]. We discuss the cosmological dynamics by considering a different class of scalar fields by taking various types of potentials and non-canonical coupling functions in various subsections. In order to obtain a concrete description of the cosmological dynamics, we shall consider a case where F(X ) = X α i.e. the noncanonical scalar field models whose Lagrangian density is given by [8,15]. Non-canonical models reduce the tensor-to-scalar ratio than their canonical counterparts, leading to a better agreement with CMB observations [52] These interesting features of non-canonical scalar fields motivate us to further investigate the cosmological dynamics of such fields in a more general context. We shall convert these cosmological equations into an autonomous system of equations and perform a dynamical system analysis for various types of f (φ) and V (φ)

Dynamical system analysis

Here we take w

Conclusion