Instability of QCD ghost dark energy model

TL;DR

This paper examines the classical instability of the ghost dark energy model in various cosmological scenarios by analyzing the sign of the squared sound speed, finding it to be negative and thus unstable against perturbations.

Contribution

It provides a comprehensive analysis of the ghost dark energy model's stability in both interacting and noninteracting cases across flat and non-flat universes.

Findings

Ghost dark energy is unstable in all examined cases due to negative squared sound speed.

Instability increases with higher interaction coupling.

The model's classical stability is not supported in the studied scenarios.

Abstract

We investigate the instability of the ghost dark energy model against perturbations in different cases. To this goal we use the squared sound speed $v_s^2$ whose sign determines the stability of the model. When $v_s^2<0$ the model is unstable against perturbation. At first we discuss the noninteracting ghost dark energy model in a flat FRW universe and find out that such a model is unstable due to the negativity of the $v_s^2$ in all epoches. The interacting ghost dark energy model in both flat and non-flat universe are studied in the next parts and in both cases we find that the squared sound speed of ghost dark energy is always negative. This implies that the perfect fluid for ghost dark energy is classically unstable against perturbations. In both flat and non flat cases we find that the instability of the model increases with increasing the value of the interacting coupling parameter.