B. C. Paul

Emergent universe with exotic matter

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.

General solution for a relativistic star

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.

Modified Chaplygin gas and constraints on its B parameter from cold dark matter and unified dark matter energy cosmological models

We study modified Chaplygin gas (MCG) as a candidate for dark energy and predict the values of parameters of the gas for a physically viable cosmological model. The equation of state of MCG (p = Bp - A/ρ α ) involves three parameters: B, A and α. The permitted values of these parameters are determined with the help of a dimensionless age parameter (H o t o ) and H(z) z data. Specifically, we study the allowed ranges of values of the B parameter in terms of and A s (A s is defined in terms of the parameters in the theory). We explore the constraints of the parameters in the cold dark matter and unified dark matter energy models, respectively.

Emergent universe scenario in the Einstein–Gauss–Bonnet gravity with dilaton

We obtain cosmological solutions which admit emergent universe (EU) scenario in the framework of Einstein Gauss–Bonnet (GB) gravity coupled with a dilaton field in 4-dimensions. The coupling parameter of the GB terms and the dilaton in the theory are determined for obtaining an EU scenario. The corresponding dilaton potential which admits such scenario is determined. It is found that the GB terms coupled with a dilaton field plays an important role in describing the dynamics of the evolution of the early as well as the late universe. We note an interesting case where the GB term dominates initially in the asymptotic past regime, subsequently it decreases and thereafter its contribution in determining the dynamics of the evolution dominates once again. We note that the Einstein’s static universe solution permitted here is unstable which the asymptotic EU might follow. We also compare our EU model with supernova data.

Constraints on Exotic Matter for An Emergent Universe

We study a composition of normal and exotic matter which is required for a flat Emergent Universe scenario permitted by the equation of state (EOS)(

Accelerating universe in modified theories of gravity

p=A\rho-B\rho^{1/2}

Constraints on exotic matter needed for an emergent universe

) and predict the range of the permissible values for the parameters

Emergent Universe from a composition of matter, exotic matter and dark energy

A

RELATIVISTIC SOLUTION FOR A CLASS OF STATIC COMPACT CHARGED STAR IN PSEUDO-SPHEROIDAL SPACETIME

and

RELATIVISTIC STRANGE STARS WITH ANISOTROPY

B