M. Sami

Dynamics of dark energy

We review in detail a number of approaches that have been adopted to try and explain the remarkable observation of our accelerating universe. In particular we discuss the arguments for and recent progress made towards understanding the nature of dark energy. We review the observational evidence for the current accelerated expansion of the universe and present a number of dark energy models in addition to the conventional cosmological constant, paying particular attention to scalar field models such as quintessence, K-essence, tachyon, phantom and dilatonic models. The importance of cosmological scaling solutions is emphasized when studying the dynamical system of scalar fields including coupled dark energy. We study the evolution of cosmological perturbations allowing us to confront them with the observation of the Cosmic Microwave Background and Large Scale Structure and demonstrate how it is possible in principle to reconstruct the equation of state of dark energy by also using Supernovae Ia observational data. We also discuss in detail the nature of tracking solutions in cosmology, particle physics and braneworld models of dark energy, the nature of possible future singularities, the effect of higher order curvature terms to avoid a Big Rip singularity, and approaches to modifying gravity which leads to a late-time accelerated expansion without recourse to a new form of dark energy.

Cosmological Dynamics of Phantom Field

We study the general features of a dynamics of a phantom field in the cosmological context. In the case of an inverse coshyperbolic potential, we demonstrate that the phantom field can successfully drive the observed current accelerated expansion of the Universe with the equation of state parameter

Dark energy cosmology from higher-order, string-inspired gravity, and its reconstruction

{w}_{\ensuremath{\varphi}}l\ensuremath{-}1.

Aspects of tachyonic inflation with exponential potential

The de Sitter universe turns out to be the late time attractor of the model. The main features of the dynamics are independent of the initial conditions and the parameters of the model. The model fits the supernova data very well, allowing for

What is needed of a tachyon if it is to be the dark energy

\ensuremath{-}2.4l{w}_{\ensuremath{\varphi}}l\ensuremath{-}1

The fate of (phantom) dark energy universe with string curvature corrections

at a 95% confidence level.

Dark energy and cosmological solutions in second-order string gravity

In this paper we investigate the cosmological effects of modified gravity with string curvature corrections added to the Einstein-Hilbert action in the presence of a dynamically evolving scalar field coupled to Riemann invariants. The scenario exhibits several features of cosmological interest for the late universe. We show that higher-order stringy corrections can lead to a class of dark energy models consistent with recent observations. The models can give rise to quintessence without recourse to a scalar field potential. The detailed treatment of the reconstruction program for general scalar-Gauss-Bonnet gravity is presented for any given cosmology. The explicit examples of reconstructed scalar potentials are given for an accelerated (quintessence, cosmological constant, or phantom) universe. Finally, the relation with modified

Avoidance of future singularities in loop quantum cosmology

F(G)

A unified approach to scaling solutions in a general cosmological background

gravity is established at the classical level and is extended to include third order terms on the curvature.

Galileon gravity and its relevance to late time cosmic acceleration

We consider issues related to tachyonic inflation with an exponential potential. We find an exact solution of the evolution equations in the slow roll limit in FRW cosmology. We also carry out a similar analysis in the case of brane assisted tachyonic inflation. We investigate the phase space behavior of the system and show that the dustlike solution is a late time attractor. The difficulties associated with reheating in the tachyonic model are also indicated.