We discuss the phenomenon of the smooth dynamical gravity induced crossing of the phantom divide line in a framework of simple cosmological models where it appears to occur rather naturally, provided the potential of the unique scalar field has some kind of cusp. The behavior of cosmological trajectories in the vicinity of the cusp is studied in some detail and a simple mechanical analogy is pr...

The physical process leading to the acceleration of the expansion of the universe is unknown. It may involve new high energy physics or extensions to gravitation. Calling this generically dark energy, we examine the consistencies and relations between these two approaches, showing that an effective equation of state function w(z) is broadly useful in describing the properties of the dark energy...

We propose wormholes solutions by assuming space dependent equation of state parameter. Our models show that the existence of wormholes is supported by phantom energy. Here, the phantom energy is characterized by variable equation state parameter. We show that the averaged null energy condition (ANEC) violating phantom energy can be reduced as desired.

We study possible crossing of the phantom divided barrier in a Lorentz invariance violating dark energy model. Lorentz invariance violation which is achieved by introducing a vector field in the action, incorporates directly in the dynamics of the scalar field and equation of state. This interesting feature allows us to study phantom divided barrier crossing in the context of Lorentz invariance...

A multidimensional cosmological model describing the dynamics of n+1 Ricci-flat factor-spaces Mi in the presence of a one-component anisotropic fluid is considered. The pressures in all spaces are proportional to the density: pi = wiρ , i = 0, ..., n . Solutions with accelerated expansion of our 3-space M0 and small enough variation of the gravitational constant G are found. These solutions exi...

We consider the interacting new agegraphic dark energy model to investigate the validity of the generalized second law of thermodynamics in non-flat universe enclosed by the apparent horizon. We show that for this model in presence of interaction with the cold dark matter, the equation of state parameter can cross the phantom divide. We also present that for the selected model under thermal equ...

We consider the problem of describing the asymptotic behaviour of FRW universes near their spacetime singularities in general relativity. We find that the Bel-Robinson energy of these universes in conjunction with the Hubble expansion rate and the scale factor proves to be an appropriate measure leading to a complete classification of the possible singularities. We show how our scheme covers al...

We formulate Hořava-Lifshitz cosmology with an additional scalar field that leads to an effective dark energy sector. We find that, due to the inherited features from the gravitational background, Hořava-Lifshitz dark energy naturally presents very interesting behaviors, possessing a varying equation-of-state parameter, exhibiting phantom behavior and allowing for a realization of the phantom d...

We consider a modified form of gravity in which the action contains a power α of the scalar curvature. It is shown how the presence of a bulk viscosity in a spatially flat universe may drive the cosmic fluid into the phantom region (w < −1) and thus into a Big Rip singularity, even if it lies in the quintessence region (w > −1) in the non-viscous case. The condition for this to occur is that th...