G. P. 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.

A new class of cosmological models in Lyra geometry

FRW models have been studied in the cosmological theory based on Lyra’s geometry. A new class of exact solutions has been obtained by considering a time dependent displacement field for constant deceleration parameter models of the universe.

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.

Gravitational energy in the expanding universe

The role of gravitational energy in the evolution of the universe is examined. In co-moving coordinates, calculation of the Landau-Lifshitz pseudotensor for FRW models reveals that: (i) the total energy of a spatially closed universe irrespective of the equation of state of the cosmic fluid is zero at all times, (ii) the total energy enclosed within any finite volume of the spatially flat universe is zero at all times, (iii) during inflation the vacuum energy driving the accelerated expansion and ultimately responsible for the creation of matter (radiation) in the universe, is drawn from the energy of the gravitational field. In a similar fashion, certain cosmological models which abandon adiabaticity by allowing for particle creation, use the gravitational energy directly as an energy source.

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.

Plane Symmetric Domain Wall in Lyra Geometry

In this paper general solutions are found for domain walls in Lyra geometry in the plane symmetric spacetime metric given by Taub. Expressions for the energy density and pressure of domain walls are derived in both cases of uniform and time varying displacement field β. It is also shown that the results obtained by Rahaman et al [IJMPD, 10, 735 (2001)] are particular case of our solutions. Finally, the geodesic equations and acceleration of the test particle are discussed.

Bulk viscosity and particle creation in Brans—Dicke theory

The efiect of bulk viscosity on the evolution of the spatially ∞at Friedmann{Lemaitre{ Robertson{Walker (FLRW) models in the context of open thermodynamical systems, which allow for particle creation, is analysed within the framework of Brans{Dicke (BD) theory. The BD fleld equations are modifled with the incorporation of a creation pressure and bulk viscous stress. A class of physically plausible models has been taken into consideration. The behaviour of the particle number density and bulk viscosity is discussed with the evolution of the Brans{Dicke scalar fleld.

String cosmology with electromagnetic fields in Bianchi-type-II, -VIII and -IX space-time

SummaryA new class of physically relevant exact cosmological solutions for massive strings in the presence of electromagnetic fields has been obtained in Bianchi-type-II, -VIII and -IX space-time. The physical and the kinematical behaviour of these models have been discussed.