International Journal of Modern Physics D

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.

The diffraction effects on gravitational waves propagating through a stellar cluster are analyzed in the relevant approximation of Fresnel diffraction limit. We find that a gravitational wave scintillation effect — similar to the radio source scintillation effect — comes out naturally, implying that the gravitational wave intensity changes in a characteristic way as the observer moves.

We study the Non-Linear Born–Infeld (NLBI) scalar field model and quintessence model with two different potentials (V(ϕ) = -sϕ and ). We investigate the differences between these two models. We explore the equation of state parameter w and the evolution of scale factor a(t) in both the NLBI scalar field and quintessence model. The present age of universe and the transition redshift are also obtained. We use the Gold dataset of 157 SN-Ia to constrain the parameters of the two models. All the results show that the NLBI model is slightly superior to the quintessence model.

A linear second-order wave equation is presented based on cosmological general relativity, which is a space-velocity theory of the expanding universe. The wave equation is shown to be exactly solvable, based on the Gaussian hypergeometric function.

We consider the anomaly induced effective action in super Yang–Mills theory in interaction with the Brans–Dicke (BD) field. The generalization of the BD theory so as to permit an energy exchange between the scalar field and ordinary matter fields, was recently worked out by T. Clifton and J. D. Barrow [Phys. Rev. D73, 104022 (2006)]. We derive the scalar field equations for the dilaton field, and the BD field, and discuss the Friedmann equation in the general case. The present paper is a continuation of an investigation few years ago dealing with the case of conformal anomaly plus ordinary classical gravity [I. Brevik and S. D. Odintsov, Phys. Lett. B455, 104 (1999)].

In the present work, we investigate the influence of the monopole field on the occurrence of the space–time singularities in the gravitational collapse of anti-de Sitter–Vaidya space–time. It has been found that the spherically symmetric monopole-anti-de Sitter–Vaidya space–time contradicts the CCH, whereas the non-spherical collapse respects it.