Related papers: K-essence and the coincidence problem
We consider a k-essence model in which a single scalar field can be responsible for both primordial inflation and the present observed acceleration of the cosmological background geometry, while also admitting a nonsingular de Sitter…
The so called `cosmic coincidence' problem seems to suggest a coupling between dark energy and dark matter. A possibility could be given by dark matter particles with masses depending exponentially on the scalar field associated to dark…
We use a simple form of the K-essence theory and apply it to the classic isotropic cosmological model and seek exact solutions. The particular form of the kinetic term that we choose is $K \left(\phi, X \right)= K_0(\phi)X^m +K_1$. The…
The present thesis is a collection of papers which deals with analytic models that can drive the present accelerated expansion of the universe, starting from a decelerated expansion in the early matter dominated regime. Both minimally and…
The coincidence problem of late cosmic acceleration constitutes a serious riddle with regard to our understanding of the evolution of the Universe. Here we argue that this problem may someday be solved -or better understood- by expressing…
By analysing the cosmological dynamical system with a dark-sector interaction which changes sign during the cosmological evolution, we find a scaling attractor to help to alleviate the cosmic-coincidence problem. This result shows that this…
Dark energy models which alter the relative scaling behavior of dark energy and matter could provide a natural solution to the cosmic coincidence problem - why the densities of dark energy and dark matter are comparable today. A generalized…
The homogeneous expansion history H(z) of our universe measures only kinematic variables, but cannot fix the underlying dynamics driving the recent acceleration: cosmographic measurements of the homogeneous universe, are consistent with…
The evolution of the quintessence in various stages of the universe, the radiation-, matter-, and quintessence-dominated, is closely related with the tracking behavior and the deceleration parameter of the universe. We gave the explicit…
Interacting quintessence models have been proposed to explain or, at least, alleviate the coincidence problem of late cosmic acceleration. In this paper we are concerned with two aspects of these kind of models: (i) the dynamical evolution…
It is a mystery why the density of matter and the density of vacuum energy are nearly equal today when they scale so differently during the expansion of the Universe. We suggest a paradigm that might allow for a non-anthropic solution to…
The present work deals with a dynamical systems study of quintessence potentials leading to the present accelerated expansion of the universe. The principal interest is to check for late time attractors which give an accelerated expansion…
A late accelerated expansion of the Universe is obtained from non-relativistic particles with a short-range attractive interaction, and low enough temperature to produce a Bose-Einstein condensate; by considering coupled dark-energy…
Neutrinos interacting with the quintessence field can trigger the accelerated expansion of the Universe. In such models with a growing neutrino mass the homogeneous cosmological solution is often unstable to perturbations. We present…
The early cosmic inflation, when taken along with the recent observations that the universe is currently dominated by a low density vacuum energy, leads to at least two potential problems which modern cosmology must address. First, there is…
In this article we try to find out the conditions when a ghost field in conjunction with a barotropic fluid produces a stable accelerating expansion phase of the universe. It is seen that in many cases the ghost field produces a condensate…
Recent astronomical observations of SNIa, CMB, as well as BAO in the Sloan Digital Sky Survey, suggest that the current Universe has entered a stage of an accelerated expansion with the transition redshift at $z \simeq 0.5$. While the…
A cosmological constant fits all current dark energy data, but requires two extreme fine tunings, both of which are currently explained by anthropic arguments. Here we discuss anti-anthropic solutions to one of these problems: the cosmic…
A novel approach to the class of cosmic barotropic fluids in which the speed of sound squared is defined as a function of the Equation of State parameter, so called $c_s^2(w)$ models, is examined. For this class of models, a new analytical…
We consider a late-time cosmological model based on a recent proposal that the infinite-bare-coupling limit of superstring/M-theory exists and has good phenomenological properties, including a vanishing cosmological constant, and a…