Bianchi type-V cosmological model with purely magnetic solution

In the present paper we study some new aspects of the Bianchi type-V space time. The Electric and Magnetic parts of Weyl tensors are calculated in terms of tilted congruence and discussed the purely magnetic Weyl tensor. Einstein field equations for purely magnetic space time are obtained and solution of such field equations called purely magnetic solution. To get deterministic solutions of the field equations we consider a new law of variation of average scale factor which yields time dependent deceleration parameter. Certain physical and geometrical properties of the model are also 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.     

Bulk viscous cosmological model

Robertson—Walker cosmological models with bulkviscosity are investigated explicitly with equation of statep=(-1). In particular, the physical nature of the extreme cases, i.e., degenerate vacuum bulkviscous fluid model and bulkviscous stiff fluid model are studied in detail.     

Tilted electromagnetic Bianchi type III cosmological solution

An exact cosmological solution to the Einstein-Maxwell equations for the case of Bianchi type III symmetry with stiff matter and an electromagnetic field is constructed. The behaviour of the solution near the singularity and at late stages of the expansion is investigated.     

Bianchi type-III cosmological model in f(R,T) theory of gravity

A spatially homogeneous Bianchi type-III space-time is considered in the presence of perfect fluid source in the frame work of f(R,T) gravity (Harko et al. in Phys. Rev. D 84:024020, 2011) with the help of a special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento B 74:182, 1983). A cosmological model with an appropriate choice of the function f(T) has been constructed. The physical behavior of the model is studied.     

A cosmological model without singularity

Based on the assumption, that potential energy of matter in a mass filled space contributes a negative term to the energy tensor, solutions of the Einstein field equations are possible that exhibit no singularities, since the action of gravity changes sign when the density of potential energy exceeds the density of mass-energy. The solution, in which potential energy and mass-energy are in balance, is identical with Einstein's static universe. It is shown that all the observational facts, that are usually considered as confirming the big bang model, as the cosmological red shift, the abundances of light elements and the existence of the microwave background radiation, can be understood also in a static world model, when it is taken into account that due to the finite velocity of gravitational interaction all moving quanta lose momentum to the gravitational tensor potential. As in the static cosmological model the overwhelming fraction of the total mass exists in form of a hot intergalactic plasma. The model gives a simple explanation for the diffuse x-ray background and a solution to the missing mass problem without invoking any kind of new physics or of yet undiscovered particles. Also the causality problem and the curvature problem posed by the energy density of the quantum mechanical vacuum fields find a natural solution.     

Inhomogeneous model with cosmological term

In this paper, by allowing both pressure and curvature, we exhibit someproperties of the cosmological models with varying cosmological term inthe framework of the Lemaítre-Tolman-Bond (LTB) metric. For thepreceding consideration we derive from Einstein's equations (EFE's) ahomogeneous and inhomogeneous solutions. The evolution of these models isexhibited.We also derive another class of solutions that give the asymptotically toexponential `inflation' type model at the infinity.     

General relativistic singularity-free cosmological model

We “explain”, using a Classical approach, how the Universe was created out of “nothing”, i.e., with no input of initial energy nor mass. The inflationary phase, with exponential expansion, is accounted for, automatically, by our equation of state for the very early Universe. This is a Universe with no-initial infinite singularity of energy density.     

Bianchi type-V bulk viscous string cosmological model in f(R,T) gravity

In this paper, we investigate a spatially homogeneous and anisotropic Bianchi type-V cosmological model in a scalar-tensor theory of gravitation proposed by Harko et al. (Phys. Rev. D 84:024020, 2011) when the source for energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. To obtain a determinate solution, a special law of variation proposed by Berman (Nuovo Cimento B 74:182, 1983) is used. We have also used the barotropic equation of state for the pressure and density and bulk viscous pressure is assumed to be proportional to energy density. It is interesting to note that the strings in this model do not survive. Also the model does not remain anisotropic throughout the evolution of the universe. Some physical and kinematical properties of the model are also discussed.     

LRS Bianchi type-I cosmological model in f(R,T) theory of gravity

The exact solutions of the field equations in respect of LRS Bianchi type-I space time filled with perfect fluid in the framework of f(R,T) gravity (Harko et al., arXiv: [gr-qc], 2011) are derived. The physical behavior of the model is studied. In fact, the possibility of reconstruction of the LRS Bianchi type-I cosmology with an appropriate choice of a function f(T) has been proved in f(R,T) gravity.     

The microwave background and (m,Z) relations in a tilted cosmological model

The structure of the cosmic microwave background temperature is studied in the context of a Bianchi type-V tilted cosmological model. First integrals of the equations for the null geodesics are found by use of the symmetries of the model, enabling the celestial temperature distribution to be found. The quadrupole and dipole moments are calculated for some models, suggesting that the observed anisotropy in the cosmic microwave background can be understood in the context of a Bianchi type-V model of the Universe. The apparent magnitude-redshift relations are also calculated for these models.     

A study on Bianchi-IX cosmological model

In this paper the inflationary solutions are studied for the Bianchi-IX space-time in presence of a massless scalar field with a flat potential. Also a class of cosmological solutions of massive strings are obtained following the techniques used by Letelier and Stachel. Some solutions are calculated for pure massive strings following the Takabayashi equation of state =(1+w).     

The cosmological model of Brans-Dicke theory

We use the generalized Brans-Dicke theory, in which the Pauli metric is identified to be the physical space-time metric, to study the Universe in different epochs. Exact analytical expressions for dilaton field , cosmological radiusR and density parameter are obtained fork=+1,0,–1 Universe in the radiation-dominated epoch. For matter dominated Epoch, exact analytical expressions for Hubble parameterH, cosmological radius, dilaton field, deceleration factorq, density parameter and the gravitational coupling of the ordinary matter are obtained for the flat Universe. Other important results are: (1) the density parameter is always less than unity for the flat Universe because the dilaton field plays a role as an effective dark matter, and (2) the new Brans-Dicke parameter must be larger than 31.75 in order to consistent with the observed data.     

Anisotropic model with decaying cosmological term

A spatially homogeneous and anisotropic locally rotationally symmetric Bianchi type-I spacetime with cosmological term \(\varLambda \) in \(f(R,T) \) theory has been studied. The exact solution of the field equations is obtained under a variation law of the Hubble parameter \((H) \) which yields a time dependent deceleration parameter (Banerjee and Das in Gen. Relativ. Gravit. 37:10, 2005). The model presents a cosmological scenario which describes early deceleration and late time acceleration. The physical parameters of the model have been analysed.     

Bianchi type VI h perfect fluid cosmological model in f(R,T) theory

In this paper, we have investigated Bianchi type VI _h cosmological model filled with perfect fluid in the framework of f(R,T) gravity, where R is the Ricci scalar and T is the trace of the energy-momentum tensor proposed by Harko et al. (Phys. Rev. D 84:024020, 2011). We have obtained the cosmological models by solving the field equations. Some physical behaviors of the model are also studied.