Kirti Mehta

In this study, we analyze the ghost dark energy model in Brans-Dicke cosmology in the framework of a flat Friedmann-Lemaitre-Robertson-Walker universe. We consider an interaction between ghost dark energy and dark matter with a sign-changeable interaction term. To discuss the cosmological implications of the model, we consider a well-motivated logarithmic form of the Brans-Dicke scalar field. By deriving the cosmological evolution equations, we obtain the cosmological parameters such as the equation of state and deceleration parameters. We analyze the behavior of the cosmological parameters by plotting their graphs against the redshift parameter ($z$). We observe that the equation of state parameter shows quintessence-like behaviour during present and future epochs; however, phantom-like behavior is also possible for suitable values of the model parameters. Analysis of the deceleration parameter shows a smooth recent phase transition of the universe (deceleration to acceleration). An interesting result we observe is the decelerated expansion of the universe in the far future, i.e, the universe experiences another phase transition in the future. The physical significance of the well-known cosmological plane ($w_D-w_D'$ plane) is discussed in our model. We observe that the trajectories start in the freezing region with the same initial behavior, deviate from each other during the evolution and ends in the thawing region. Finally, we perform a detailed thermodynamic analysis and demonstrate that the generalized second law of thermodynamics is satisfied within the present interacting ghost dark energy model.

In this paper, we present a comprehensive analysis of the holographic dark energy model with Granda–Oliveros cutoff in Brans–Dicke theory. We assume that the scalar field has a logarithmic form [ ], where a is the scale factor, [ ] and [ ] are arbitrary constants. The evolution of the universe is discussed by calculating the equation of state parameter [ ] of holographic dark energy and deceleration parameter q. To discuss the cosmography of the model, we calculate the value of the Hubble parameter [ ] and constrain the model parameters using recent observational data sets. The best fit value of Hubble constant [ ] has been obtained which shows agreement with the recent observations. We plot graphs of [ ] and q using the best fit values of the parameters which depict their evolution against the redshift parameter z. The graphs show that the model explains the recent phase transition of the universe. We observe an interesting result which shows a decelerating universe in the far future. It is observed that [ ] does not cross the phantom divide line, i.e. the model is free from a big-rip singularity. The statefinder analysis shows, however, the model trajectory lies in the quintessence region for quite a long period, but the overall evolution is different from known dark energy models. We apply a thermodynamic analysis and find that the generalized second law of thermodynamics holds in the model for the best fit values of the parameters. We verify the stability of the model using the squared sound speed method and find that the model is stable. Moreover, we study the energy conditions for the present model. We observe that the strong energy condition is violated during the present epoch and in the future. However, we observe that it is again satisfied in the vicinity of the point [ ]. The null energy condition remains satisfied throughout which shows consistency with the behavior observed in the [ ]-CDM model.