Cosmological implications of dark energy models in modified gravity

We discuss the interacting modified QCD ghost dark energy and generalized ghost pilgrim dark energy with cold dark matter in the framework of dynamical Chern–Simons modified gravity. We investigate the cosmological parameters such as Hubble parameter, deceleration parameter and equation of state. We also discuss the physical significance of various cosmological planes like [Formula: see text] and statefinders. It is found that the results of cosmological parameters as well as planes explain the accelerated expansion of the Universe and are compatible with observational data.

COSMOGRAPHY OF INTERACTING GENERALIZED QCD GHOST DARK ENERGY

Exploring the accelerated expansion of the universe, we investigate the generalized ghost dark energy (GGDE) model from the statefinder diagnostic analysis in a flat Friedmann–Robertson–Walker universe. First, we calculate the cosmological evolution and statefinder trajectories for noninteracting case and then extend this work by considering the interaction between dark matter and dark energy components. We show that in the noninteracting case the phantom line cannot be crossed and also the evolutionary trajectories of model in s - r plane cannot be discriminated. It has been shown that the present location of model in s - r plane would be close to observational value for negative values of the model parameter. In the presence of interaction between dark matter and dark energy, the phantom regime is achieved, the accelerated phase of expansion occurs sooner compared with the noninteracting case. The GGDE model is also discussed from the viewpoint of perturbation theory by calculating the adiabatic sound speed of the model. Finally, unlike the noninteracting case, the evolutionary trajectories in s - r plane can be discriminated in the interacting model. Like the noninteracting model, in the interacting case the present location of GGDE model is closer to observational value for negative values of the model parameter.

INSTABILITY OF QCD GHOST DARK ENERGY MODEL

We investigate the instability of the ghost dark energy model against perturbations in different cases. To this goal we use the squared sound speed [Formula: see text] whose sign determines the stability of the model. When [Formula: see text] 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 [Formula: see text] in all epoches. The interacting ghost dark energy model in both flat and nonflat 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.