On purely magnetic diagonal Bianchi type VI h cosmologies

A class of purely magnetic diagonal Bianchi type VI _h Cosmologies is investigated. If the energy-momentum tensor is specialized to that of a perfect fluid with (non-zero) heat-flux, with respect to the co-moving fluid 4-velocity, then the only solution is of Bianchi type V and un-physical. Further, it is shown that if certain metric functions are functionally related then the spacetime is conformally flat. Unfortunately, all these results (somewhat indirectly) invalidate a claim by Kumar and Srivastava of finding a non-conformally flat purely magnetic diagonal Bianchi type V cosmology. Finally, we consider non-zero anisotropic pressure in place of non-zero heat flux. It is shown that these spacetimes are necessarily Bianchi type VI ₀. We highlight the fact that there is a known solution that generalizes the purely magnetic perfect fluid Wylleman-Van den Bergh spacetime. Physical properties of this solution are discussed.     

Bianchi type-VI0 conformally invariant scalar fields

An exact solution of Einstein's equations corresponding to the conformally invariant scalar field with tracefree energy-momentum tensor as source is obtained in Bianchi type VI₀ class of metrics. The solution represents a spatially homogeneous but anisotropy universe which admits anisotropic expansions. Some properties of the cosmological model are discussed.     

Anisotropic viscous-fluid cosmological model

We present exact solutions of a Bianchi type VI₀ viscous fluid cosmological model. It is a generalization of the model proposed by Banerjee and Santos (1983) for Bianchi type I.     

Comment on the vacuum Bianchi type I solution in the Brans-Dicke theory

We wish to point out that the axialsymmetric Bianchi type I vacuum solution recently given by Ram, is wrong. Moreover, the correct solution is only a special case of the general triaxial Bianchi type I solution given by Ruban and Finkelstein.     

Inhomogeneous generalizations of Bianchi type VIh models with perfect fluid

Inhomogeneous universes admitting an AbelianG ₂ of isometry and filled with perfect fluid have been derived. These contain as special cases exact homogeneous universes of Bianchi type VI_h.Many of these universes asymptotically tend to homogeneous Bianchi VI_h universes. The models have been discussed for their physical and kinematical behaviours.     

Exact Bianchi type-VI0 vacuum cosmological model in Brans-Dicke theory

We present an exact solution of the vacuum Brans-Dicke field equations for cosmological models of Bianchi type-VI₀. The solution represents anisotropic universe which has no analogy in Einstein's theory.     

Inhomogeneous generalisation of Bianchi type-VIo cosmological model of perfect fluid distribution in general relativity

Einstein's equations have been solved for perfect fluid distribution. The solution obtained may be considered as inhomogeneous generalisation of Bianchi type-VI_o cosmological model.     

Spatially self-similar cosmological model of Bianchi type-1I

The Einstein equations are integrated for a tilted spatially self-similar Bianchi type-₁I space-time with ‘stiff’ matter content. The solution represents an anisotropic model which tends to isotropic expansion in a special case.     

Comment on the inhomogeneous Bianchi type-VI0 solution

The inhomogeneous Bianchi type-VI₀ perfect fluid solution given recently by Roy and Narain (1985) is shown to be identical with the solution first given by Tomita (1978).     

Bianchi type I vacuum,field in Brans-Dicke theory

An exact solution of the vacuum Brans-Dicke field equations is obtained for the metric tensor of a spatially-homogeneous and anisotropic Bianchi type I configuration. The solution has no analogy in Einstein's theory for the layer values of the BD parameter. Some properties of the solution are discussed.     

Tilted electromagnetic Bianchi type VIo cosmological model

The Einstein-Maxwell equations are integrated for a tilted Bianchi type VI_o space-time with stiff matter and an electromagnetic field. The solution represents an anisotropic homogeneous cosmological model which tends to isotropic expansion.     

LRS Bianchi type V vacuum cosmological solution in Brans-Dicke theory

In this note a new solution of the BD field equations, for a Bianchi type V space-time, is obtained. The solution has its general relativistic analogue. Some properties of the solution are also discussed.     

On Some Bianchi Type Cosmological Models in a Bimetric Theory of Gravitation

Spatially-homogeneous and anisotropic Bianchi type-III, V, VI₀ cosmological models in Rosen's (1973) bimetric theory of gravitation are considered. It is shown that, in each case, when the soure of the gravitation field is a perfect fluid distribution Bianchi type cosmological models do not exist. Hence vacuum models are presented and studied. This revised version was published online in July 2006 with corrections to the Cover Date.     

Bianchi type-VI0 cosmological models with anisotropic dark energy

The anisotropic nature of the dark energy for Bianchi type-VI₀ space time is discussed. The exact solution of the Einstein field equations under the assumption on the anisotropy of the fluid are obtained for exponential and power-law volumetric expansions. The isotropy of the fluid, space and expansion are examined.     

Some Bianchi-type cosmological models in a new scalar-tensor theory

Bianchi type I, III, V, VI₀, and Kantowski-Sachs type models have been investigated in a scalar tensor theory developed by Saez and Ballester (1985) and Saez (1985). The dynamical behaviour of the models has also been analyzed.     

A cosmological model with both deceleration and acceleration

In this paper, we investigate a variation law for Hubble’s parameter in the curved, expanding background of spatially homogeneous, anisotropic Bianchi type I space-time. By choosing a particular form of the generalized Hubble’s parameter, which gives an early deceleration and late time acceleration for the anisotropic Bianchi type I cosmological model, we show that the model approaches isotropy and tends to a de Sitter universe at late times. The cosmological term asymptotically tends to a genuine cosmological constant and the solution is consistent with recent observations.     

General vacuum solution for Brans-Dicke-Bianchi type-II

In this paper we have obtained the general vacuum solution for Bianchi type-II in the Brans-Dicke theory for total anistropyR ₁R ₂R ₃. It is known that by use of our method, we can find the general solution for Bianchi type-II vacuum case in the general relativity theory, first given by Taub (1951). Some physical properties of this model are also discussed.     

Dynamics of a magnetized Bianchi VI 0 universe with anisotropic fluid

We discuss spatially homogeneous and anisotropic Bianchi type VI ₀ cosmological model with anisotropic fluid and magnetic field. The energy-momentum tensor consists of anisotropic fluid with anisotropic EoS and a uniform magnetic field of energy density ρ _B . Exact solution of the field equations is obtained by using the condition that expansion is proportional to the shear scalar. We focus on the future evolution of the model both in the presence and absence of magnetic field. In particular, we address the question whether these models approach to isotropy.     

Vacuum bianchi type V and VI0 cosmological models in a new scalar-tensor theory of gravitation

Vacuum Bianchi type V and VI₀ cosmological models obtained in a new scalar-tensor theory of gravitation proposed by Schmidtet al. Some physical properties of these models are also discussed.     

Holographic dark energy model with linearly varying deceleration parameter and generalised Chaplygin gas dark energy model in Bianchi type-I universe

The paper deals with a spatially homogeneous and anisotropic Bianchi type-I universe filled with two minimally interacting fluids; matter and holographic dark energy components. The nature of the holographic dark energy for Bianchi type-I space time is discussed. An exact solution to Einstein’s field equations in Bianchi type-I line element is obtained using the assumption of linearly varying deceleration parameter. Under the suitable condition, it is observed that the anisotropy parameter of the universe approaches to zero for large cosmic time and the coincidence parameter increases with increasing time. We established a correspondence between the holographic dark energy models with the generalised Chaplygin gas dark energy model. We also reconstructed the potential and dynamics of the scalar field which describes the Chaplygin cosmology. Solution of the field equations shows that a big rip type future singularity will occur for this model. It has been observed that the solutions are compatible with the results of recent observations.