Instability of QCD ghost dark energy model

Understand

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.