Tarkeshwar Singh

Bianchi type‐I cosmological models in Lyra’s geometry

Exact solutions are obtained for the anisotropic Bianchi type‐I model in normal gauge for Lyra’s geometry. The physical behavior of the models is examined in vacuum and in the presence of perfect fluids.

Bianchi type III and Kantowski-Sachs cosmological models in lyra geometry

Cosmological models for Bianchi type III and Kantowski-Sachs space-times within the framework of Lyra geometry are obtained. The physical behavior of the models is also discussed.

Higher-dimensional cosmological model with variable gravitational constant and bulk viscosity in Lyra geometry

We have studied five-dimensional homogeneous cosmological models with variableG and bulk viscosity in Lyra geometry. Exact solutions for the field equations have been obtained and physical properties of the models are discussed. It has been observed that the results of new models are well within the observational limit.

Some cosmological models with constant deceleration parameter

SummaryBerman (1983) presented a law of variation of Hubble’s parameter that yields constant deceleration parameter models of the Universe. In this paper, Robertson-Walker models have been studied in Einstein’s theory with cosmological term and in cosmological theory based on Lyra’s geometry. Some simple models have been obtained. The necessary relations in each model have been derived, considering a perfect fluid.

String cosmological models with magnetic field

A new class of string cosmological models withand without magnetic field in the context of aspace-time with G3 symmetry has beenpresented. In order to study the effects of magneticfield, the standard energy-momentum tensor is modified byincorporating additional term due to magnetic field. Thephysical and kinematical behaviours of the stringcosmological models have been discussed.

New solutions for charged anisotropic fluid spheres in general relativity

SummaryThe general analytical solutions for charged fluid distribution with anisotropic pressure are obtained. These solutions depend on an arbitrary generating function and the choice of an anisotropic function which measures the degree of anisotropy. As an illustration of the procedure some physically important examples are considered.

Static anisotropic fluid spheres in general relativity with nonuniform density

An Ansatz developed by Maharaj and Maartens is used to obtain solutions of Einsteins field equations for static anisotropic fluid spheres with nonuniform density. These solutions are matched with the Schwarzschild exterior solution.

Birkhoff‐type theorem in self‐creation cosmology

It is shown that an analog of Birkhoff’s theorem of general relativity exists in a self‐creation theory of gravitation, proposed by Barber, when the scalar field is independent of time.

AN ANISOTROPIC COSMOLOGICAL MODEL IN BRANS-DICKE THEORY

Solutions of Brans-Dicke field equations are obtained when the source of the gravitational field is a perfect fluid with pressure equal to energy density and the metric is cylindrically symmetric of Marder-type. Various physical and geometrical properties of the model have been discussed. Finally the solutions have been transformed to the original form of Brans-Dicke (1961) theory and then through unit transformation to a general form.

Bianchi type V and VI0 cosmological models in Lyra geometry

The Bianchi type V and VI0 models have been investigated in Lyra geometry in both the cases with the gauge function β is a time dependent and β=constant. The physical behaviour of these models has been discussed.