Revisiting purely kinetic k-essence

TL;DR

This paper rigorously analyzes purely kinetic k-essence models using dynamical systems, confirming they cannot unify dark matter and dark energy or match observational data on cosmic structure.

Contribution

It provides a comprehensive phase space analysis including stability conditions, clarifying the limitations of purely kinetic k-essence models.

Findings

Models cannot unify dark matter and dark energy.

Models are inconsistent with observed cosmic structure.

Dynamical analysis confirms previous qualitative assessments.

Abstract

In this paper, we perform a dynamical systems study of the purely kinetic k-essence. Although these models have been studied in the past, a full study of the dynamics in the phase space incorporating the stability conditions for theoretical consistency is lacking. Our results confirm in a very rigorous and clear way that these models i) can not explain in a unified way the dark matter and dark energy components of the cosmic fluid and ii) are not adequate to explain the existing observational evidence, in particular the observed amount of cosmic structure.