Narrow Results

Making use of the generalized form of the Ghost dark energy density, which has the functional form ${\rho }_G=f(H,H^2)$ where $H$ represents the Hubble expanding rate, the present accelerated enlargement behavior of the cosmos is investigated from the Rastall theory perspective. After finding a relation for the Hubble cosmic expansion rate, we consider recent cosmology-independent measurements calculated for the expansion history of the cosmos to fit the model via the ${\chi }^2$-analysis. Moreover, we discuss the cosmographic properties of the model with the help of some cosmological quantities. We show that our model is stable and consistent with the recent astrophysical data. Also, for our model, we investigate cosmological interpretations of thermodynamics.

In this paper, we investigate ghost dark energy model in the presence of nonlinear interaction between dark energy and dark matter. We also extend the analysis to the so-called generalized ghost dark energy (GGDE) which ${\rho }_D=\alpha H+\beta H^2$. The model contains three free parameters as ${\mathrm{\Omega }}_D,\zeta (=\frac{8\pi G\beta }{3})$ and $b^2$ (the coupling coefficient of interactions). We propose three kinds of nonlinear interaction terms and discuss the behavior of equation of state, deceleration and dark energy density parameters of the model. We also find the squared sound speed and search for signs of stability of the model. To compare the interacting GGDE model with observational data sets, we use more recent observational outcomes, namely SNIa from JLA catalog, Hubble parameter, baryonic acoustic oscillation and the most relevant CMB parameters including, the position of acoustic peaks, shift parameters and redshift to recombination. For GGDE with the first nonlinear interaction, the joint analysis indicates that ${\mathrm{\Omega }}_D=0.7192\pm 0.0062$, $b^2=0.146_{-0.026}^{+0.030}$ and $\zeta =0.104\pm 0.047$ at 1 optimal variance error. For the second interaction, the best fit values at $1\sigma$ confidence are ${\mathrm{\Omega }}_D=0.72091\pm 0.0065$, $b^2=0.0395\pm 0.0080$ and $\zeta \le 0.0173$. According to combination of all observational data sets considered in this paper, the best fit values for third nonlinearly interacting model are ${\mathrm{\Omega }}_D=0.7287\pm 0.0062$, $b^2=0.0109\pm 0.0023$ and $\zeta \le 0.00764$ at $1\sigma$ confidence interval. Finally, we found that the presence of interaction is compatible in mentioned models via current observational datasets.

We study the cosmological consequences of the ghost models of dark energy (DE) in the framework of Hořava–Lifshitz gravity. We calculate the equation-of-state parameter, the deceleration parameter, the classical stability and the dimensionless density parameter of the models in both noninteracting and interacting scenarios. We find that, for some values of the parameter, this model can admit a transition from the deceleration phase to the accelerated phase around $z\approx 0.6$, while at the late time ($z\to -1$) we have ${\omega }_D\to -1$ meaning that this model mimics a cosmological constant. We find that in the setup of Hořava–Lifshitz gravity, ghost dark energy (GDE) models are classically unstable. We observe that unlike the generalized ghost dark energy (GGDE), the ghost dark energy cannot provide proper behavior for all the cosmological parameters simultaneously, with the same values of the models’ couplings.

In this paper, we determine the exact solutions of viscous ghost models in sign-changeable interaction scenarios for two choices of bouncing scale factor, assuming the existence of viscous interacting fluid across the flat Friedmann–Robertson–Walker universe in the form of ghost dark energy and pressure-less dark matter. The study demonstrates how the cosmological parameters evolve in viscous sign-changeable interacting scenarios to see the transition time frame. Next, a bounce inflation model is investigated, including the tensor-to-scalar ratio, scalar spectral index, and slow-roll parameters analytical results. Since inflation is usually associated with scalar fields, the study looked at a possible relationship between sign-changeable interacting ghost dark fluids and scalar field models. Lastly, the applicability of the generalized second law (GSL) of thermodynamics is examined for the scenarios that are being studied.