Plane symmetric cosmological models with negative constant deceleration parameter in self creation theory

In this paper, we have investigated plane symmetric cosmological models with negative constant deceleration parameter in Barber’s (Gen. Relativ. Gravit. 14:117, 1982) second self-creation theory in presence of perfect fluid source. For this we use a special law of variation for Hubble parameter proposed by Bermann (Nuovo Cim. B 74:182, 1983) that yields a constant deceleration parameter model of the universe. Some physical properties of the models and entropy are discussed and 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.     

Determinations of the cosmological deceleration parameter based on various quasar subsets

Published determinations of the deceleration parameter qo based on various selected subsets are reviewed and a uniform re-determination is made according to a procedure given in /1/.The resulting q₀-values from 8 largely independant samples of radio quasars all fall within the 4σ range obtained in /1/, namely, 1.0 ? q₀ ? 3.5. The most important assumption made is that the characteristic luminosity of radio quasars is independant of the cosmic epoch. Thus, unless radio quasars at earlier times were much more luminous than the later ones, the universe is probably closed.     

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).     

Bianchi type-V cosmological model with perfect fluid using negative constant deceleration parameter in a scalar tensor theory based on Lyra Manifold

An exact Bianchi type-V perfect fluid cosmological model is obtained in a scalar tensor theory proposed by Sen (Z. Phys. 149:311, 1957) based on Lyra Manifold in case of β is a constant and it is shown that this cosmological model exists only in the case of Radiation Universe (ρ=3p) if β is a function of ‘t’ using negative constant deceleration parameter. Some physical and geometrical properties of these models are discussed.     

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.     

Uniform anisotropic cosmological model with string source

By adopting the comoving coordinate system, the axially symmetric models with string dust cloud source are obtained. Some of these models are singular free even at an initial epoch, where the geometric as well as thep-strings become singular.     

Shear-free homogeneous cosmological model with heat flux

We present the condition of vanishing shear in a spatially homogeneous spacetime in terms of the Ricci rotation co-efficients corresponding to an orthonormal tetrad (ν ^α. _A η ^α) (whereν ^α is the unit vector along the time axis and _A η ^α are the three independent reciprocal group vectors). Assuming that the velocity vector can be expanded in the direction ofν ^α and any one of the _A η ^α’s it is shown that shear-free motion is possible only in case of some special Bianchi types, and these cases are studied assuming the velocity vector to be geodetic and that there may be a nonvanishing heat flux term.     

A plane symmetric cosmological model in Lyra manifold

A non-static plane-symmetric cosmological model in Lyra's manifold is obtained when the source of the gravitational field is a perfect fluid with pressure equal to energy density. Some properties of the model have also been 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.     

The effect of intergalactic dust on the measurement of the cosmological deceleration parameterq 0

In a recent attempt to explain the cosmic microwave background without the big bang, a thermalization mechanism involving intergalactic whisker grains of graphite was proposed. The effect of absorption by the intergalactic medium in general, and of the above type in particular, on the measurement of the deceleration parameterq ₀ of the expanding universe is discussed. Its effect is shown to be comparable in magnitude but opposite to that of the luminosity evolution in galaxies. A consequential selection effect is also discussed.     

A plane-symmetric inhomogeneous cosmological model of perfect fluid distribution with electromagnetic field

A plane-symmetric inhomogeneous cosmological model of perfect fluid distribution with electromagnetic field, is obtained.F ₁₂ is the non-vanishing component of the electromagnetic field tensor. To get a determinate solution, we assume the free gravitational field is Petrov type-II non-degenerate. In general, the model represents an expanding, shearing, non-rotating universe in which the flow vector is geodetic. The behaviour of the electromagnetic field tensor together with some geometrical and physical aspect of the model are also discussed.     

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.     

An alternative classical cosmological model with inflationary expansion

We propose a cosmological model of the Universe based on the Newtonian mechanics and classical field theory. The essential ingredient of this model is the existence of a special kind of physical field in the Universe whose source is the mass current. In the early Universe this field reached such large values that it produced matter from the vacuum fluctuation. The classical dynamical equations for the co-moving sphere in the presence of this field are enlarged by a new term which causes an inflation-like expansion. It accounts also for the hot initial stage of the early Universe and has several important cosmological consequences.     

A gravitationally non-degenerate cosmological model with expanding and shearing viscous fluid in general relativity

The object of this paper is to investigate the behaviour of viscosity in a cosmological model, in which the coefficient of shear viscosity is assumed to be proportional to rate of expansion in the model. The behaviour of the model in the absence of shear viscosity is also discussed.     

A class of cosmological solutions of Brans-Dicke theory with cosmological constant

We present a class of exact cosmological solutions of Brans-Dicke (B-D) equations with cosmological constant in flat Robertson-Walker metric. These solutions are based on the relation øR ⁿ= constant between the B-D field and the scale factor of the universe. This relation turns out to be consistent with the equation of statep =m for the cosmic matter, provided thatn andm are suitably related to each other. Several special cases and asymptotic solutions are derived and discussed.     

A static conformally flat cosmological model in Lyra's manifold

A static conformally flat spherically-symmetric perfect fluid cosmological model based on Lyra's modified Riemannian geometry is proposed. Some properties of the model are discussed.