J. K. Singh

Some spatially homogeneous string cosmological models

The Einstein field equations of massive strings are solved completely with and without a source free magnetic field for the Bianchi type I metric in a different basic form. Some physical properties of the models are studied.

Constraints on cosmological parameters in power-law cosmology

In this paper, we examine observational constraints on the power law cosmology; essentially dependent on two parameters H0 (Hubble constant) and q (deceleration parameter). We investigate the constraints on these parameters using the latest 28 points of H(z) data and 580 points of Union2.1 compilation data and, compare the results with the results of ΛCDM . We also forecast constraints using a simulated data set for the future JDEM, supernovae survey. Our studies give better insight into power law cosmology than the earlier done analysis by Kumar [arXiv:1109.6924] indicating it tuning well with Union2.1 compilation data but not with H(z) data. However, the constraints obtained on and i.e. H0 average and q average using the simulated data set for the future JDEM, supernovae survey are found to be inconsistent with the values obtained from the H(z) and Union2.1 compilation data. We also perform the statefinder analysis and find that the power-law cosmological models approach the standard ΛCDM model as q → −1. Finally, we observe that although the power law cosmology explains several prominent features of evolution of the Universe, it fails in details.

Cosmological models in certain scalar-tensor theories

AbstractExact solutions of Einstein field equations are obtained in the scalar-tensor theories developed by Saez and Ballester (1985) and Lau and Prokhovnik (1986) when the line-element has the form

String cosmological models of Bianchi type-III

ds^2 = \exp \left( {2h} \right)dt^2 - \exp \left( {2A} \right)\left( {dx^2 + dy^2 } \right) - \exp \left( {2B} \right)dz^2

Modified Chaplygin gas cosmology with statefinder diagnostic in lyra geometry

whereh, A andB are functions oft only. The solutions are spatially homogeneous, locally rotationally symmetric and admit a Bianchi I group of motions on hypersurfacest = constant. The dynamical behaviours of these models have also been discussed.

SOME COSMOLOGICAL MODELS IN SCALAR–TENSOR THEORIES

Exact nonstatic solutions to Einstein field equations are obtained for the plane symmetric spacetime filled with viscous perfect fluid in the presence of attractive scalar fields. Some physical and geometrical properties of the model are studied. The solutions characterize strong interaction of elementary particles.

SOME BIANCHI TYPE-V COSMOLOGICAL MODELS IN BRANS–DICKE THEORY

A technique to generate new exact Bianchi type-III cosmological solutions of massive strings in the presence of magnetic field is presented. Starting from Tikekar and Patels strings models in the absence and presence of the magnetic field, new solutions are obtained. Some of their physical features are discussed.

A study on totally anisotropic Bianchi type-II space-time

A procedure to generate new exact solutions to Einstein equations for perfect fluids is applied to LRS Bianchi type I line-element. Starting from some known solutions a class of new perfect fluid solutions of Bianchi type I are presented. The physical and kinematical properties of spatially homogeneous and anisotropic cosmological models are studied.