Naresh Dadhich

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

Emergent universe with exotic matter

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

Why do naked singularities form in gravitational collapse? II

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

General solution for a relativistic star

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

Characterization of the Lovelock gravity by Bianchi derivative

at a 95% confidence level.

A class of cylindrically-symmetric models in string cosmology

A general framework for an emergent universe scenario has been given which makes use of an equation of state. The general features of the model have also been studied and some possible primordial compositions of the universe have been suggested.

Matter without matter: Kaluza-Klein spacetime in Einstein-Gauss-Bonnet gravity

We investigate what are the key physical features that cause the development of a naked singularity, rather than a black hole, as the end-state of spherical gravitational collapse. We show that sufficiently strong shearing effects near the singularity delay the formation of the apparent horizon. This exposes the singularity to an external observer, in contrast to a black hole, which is hidden behind an event horizon due to the early formation of an apparent horizon.

On the static Lovelock black holes

In a spherically symmetric spacetime we find the general solution for a relativistic star in hydrostatic equilibrium having the spheroidal geometry for the 3-space embedded in 4-Euclidean space. The parameter is the measure of spheroidal character and determines the physical properties of the star. It has a lower bound ; stars with smaller mass to radius ratio can occur for all allowed while ultracompact stars, having ratios between 1/3 and 1/2, will have . It turns out that a wide range of values of can represent objects with the fluid density of a neutron star. The model is shown to possess all the desirable physical features.

Gravitational collapse of null fluid on the brane

We prove the theorem: The second-order quasilinear differential operator as a second-rank divergence-free tensor in the equation of motion for gravitation could always be derived from the trace of the Bianchi derivative of the fourth-rank tensor, which is a homogeneous polynomial in curvatures. The existence of such a tensor for each term in the polynomial Lagrangian is a new characterization of the Lovelock gravity.

Curvature-driven acceleration: a utopia or a reality?

A new class of physically relevant explicit solutions for string cosmological models endowed with cylindrical symmetry on the background of singularity-free cosmological space times has been obtained and their physical and kinematical features are discussed. The matter-free limits of this class of solutions are observed to be the singularity-free vacuum solutions of Patel and Dadhich.