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We carry out an analysis of the cosmological perturbations in general relativity for three different models which are good candidates to describe the current acceleration of the Universe. These three set-ups are described classically by…
Depending on the choice of its potential, the scalar phantom field $\phi$ (the equation of state parameter $w<-1$) leads to various catastrophic fates of the universe including big rip, little rip and other future singularity. For example,…
Various cosmological models in frames of $F(T)$ gravity are considered. The general scheme of constructing effective dark energy models with various evolution is presented. It is showed that these models in principle are compatible with…
Motivated by condensed matter physical systems, in which a finite-time singularity indicates that the topology of the system changes, we critically examine the possibility of the Universe's topology change at a finite-time cosmological…
Brane dark energy cosmologies, leading to various possible evolutions of our universe, are investigated. The discussion shows that while all these models can be made arbitrarily close to the standard $\Lambda$CDM cosmology at present, their…
Cosmological observations of the recent universe suggest that dark energy equation of state parameter $w$ is growing with time, departing from a cosmological constant for which $w=-1$. Standard quintessence models allow for a varying…
We consider the problem of describing the asymptotic behaviour of \textsc{FRW} universes near their spacetime singularities in general relativity. We find that the Bel-Robinson energy of these universes in conjunction with the Hubble…
Understanding the late-time acceleration of the universe and its subtleties is one of the biggest mysteries in cosmology. A lot of different approaches have been put forward to deal with this, ranging from the conventional cosmological…
The presence of phantom dark energy in brane world cosmology generates important new effects, causing a premature Big Rip singularity when we increase the presence of extra dimension and considerably competing with the other components of…
Properties of Braneworld models of dark energy are reviewed. Braneworld models admit the following interesting possibilities: (i) The effective equation of state can be w < -1 as well as w > -1. In the former case the expansion of the…
Using the spectacular new high redshift supernova observations from the HST/GOODS program and previous supernova, CMB and galaxy clustering data, we make the most accurate measurements to date of the dark energy density rho_X as a function…
We consider finite-time, future (sudden or Big Rip type) singularities which may occur even when strong energy condition is not violated but equation of state parameter is time-dependent. Recently, example of such singularity has been…
I point out that an effective upper limit of approximately 20 Gyr (for a Hubble constant of 72 km/s/Mpc) or alternatively on the $H_0$-independent quantity $H_0t_0 < 1.47$, exists on the age of the Universe, essentially independent of the…
By studying the present cosmological data, particularly on CMB, SNeIA and LSS, we find that the future fate of the universe, for simple linear models of the dark energy equation-of-state, can vary between the extremes of (I) a divergence of…
This paper contains a detailed discussion on new cosmic solutions describing the early and late evolution of a universe that is filled with a kind of dark energy that may or may not satisfy the energy conditions. The main distinctive…
The existence of phantom energy in a universe which evolves to eventually show a big rip doomsday is a possibility which is not excluded by present observational constraints. In this letter it is argued that the field theory associated with…
Different approaches to quantum cosmology are studied in order to deal with the future singularity avoidance problem. Our results show that these future singularities will persist but could take different forms. As an example we have…
The late-time evolution behavior of the autonomous system in the SO(1,1) dark energy model with power-law potential is studied. Big Rip may be a critical point of the autonomous system. This means that such a Big Rip may be considered as…
Some analysis of the supernovae type Ia observational data seems to indicate that the Universe today is dominated by a phantom field, for which all energy conditions are violated. Such phantom field may imply a singularity in a future…
The main characteristic of the dark energy is its negative pressure. In a homogeneous and isotropic FRW background, we consider several models for the dark energy fluid, which lead to finite time future singularities of the type I-IV, by…