Bianchi type-III bulk viscous string cosmological model in Brans-Dicke theory of gravitation

A spatially homogeneous and anisotropic Bianchi type-III space-time is considered in the framework of a scalar-tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124:925, 1961) in the presence of bulk viscous fluid containing one dimensional cosmic strings. We have found a determinate solution of the field equations using the plausible physical conditions (i) a barotropic equation state for the pressure and density, (ii) special law of variation for Hubble’s parameter proposed by Berman (Nuovo Cimento B74:182, 1983), (iii) shear scalar is proportional to scalar expansion and (iv) the trace of the energy tensor of the fluid vanishes. We have also assumed that bulk viscous pressure is proportional to energy density. Some physical and kinematical properties of the model are, also, discussed.     

Axially symmetric string cosmological models in Brans-Dicke theory of gravitation

Axially symmetric string cosmological models are obtained in a scalar- tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124:925, 1961). Some physical and geometrical properties of the models are also discussed. The models are anisotropic and free from singularities.     

A five dimensional Kaluza-Klein bulk viscous string cosmological model in Brans-Dicke scalar-tensor theory of gravitation

In this paper, we have investigated a five dimensional Kaluza-Klein space-time in the frame work of Brans-Dicke (Phys. Rev. 124:925, 1961) scalar-tensor theory of gravitation when the source of energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. We have obtained a determinate solution of the field equations using the special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento B 74:182, 1983) We have also used a barotropic equation of state for the pressure and density. Some physical properties of the model are also discussed.     

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.     

String cosmological models in five dimensional bimetric theory of gravitation

Five-dimensional spherically symmetric space-time is considered in bimetric theory of gravitation formulated by Rosen (Gen. Rel. Grav. 4, 435, 1973) in the presence of cosmic string dust cloud. Exact cosmological models which represent geometric (Nambu) string, p-string (Takabayasi string) and Reddy string (Astrophys. Space Sci. 301, 2006) are obtained in the static and non-static cases. Some physical properties of the models are also discussed.     

An anisotropic cosmological model in Brans-Dicke theory

Solutions of Brans-Dicke field equations are obtained when the source of the gravitational field is a perfect fluid with pressure equal to energy density and the metric is cylindrically symmetric of Marder-type. Various physical and geometrical properties of the model have been discussed. Finally the solutions have been transformed to the original form of Brans-Dicke (1961) theory and then through unit transformation to a general form.     

A bianchi type-III cosmological model in Brans-Dicke theory for vacuum field

An exact solution of Brans-Dicke (B-D) field equations for the metric tensor of a spatially homogeneous Bianchi type-III configuration has been obtained for vacuum field. It is shown that in the limiting case the solution reduces to that of Einstein field equations in vacuum.     

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.     

Exact Bianchi type-I cosmological model with matter in Brans-Dicke theory

In this paper an exact solution of the Brans-Dicke field equations in the presence of stiff matter is obtained for the Bianchi type-I cosmological space-time. The new solution represents an anisotropic homogeneous cosmological model which tends to anisotropic expansion. The behaviour of the solution near the singularities and late stages of the expansion is 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.     

String cosmology with Brans-Dicke theory

In this paper string cosmology has been developed in the presence of Brans-Dicke scalar field coupled to Einstein gravity. Solutions are obtained for both geometric andp-string models and physical situations are discussed.     

A string cosmological model in a scalar – Tensor theory of gravitation

An exact Boanchi type -I string cosmological model is obtained in a scalar-tensor theory of gravitation proposed by Saez and Ballester (1985). Some physical properties of the model are also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Bianchi type-II, VIII & IX perfect fluid magnetized cosmological models in Brans-Dicke theory of gravitation

Spatially homogeneous Bianchi type-II, VIII & IX charged perfect fluid cosmological models in Brans-Dicke theory of gravitation are obtained and presented. Various physical and geometrical features of the models are also discussed.     

An anisotropic cosmological model in a scalar-tensor theory of gravitation

A spatially-homogeneous and anisotropic-cosmological model in a scalar-tensor theory proposed by Sen and Dunn (1971) is obtained when the source of the gravitational field is a perfect fluid with pressure equal to energy density and the metric is of Bianchi type-I. Various physical properties of the model have also been discussed.     

An inflationary cosmological model in Dunn's scalar-tensor theory of gravitation

The gravitational field equations in Dunn's scalar-tensor theory of gravitation are generalized by including a cosmological constant. The resulting equations are solved for a Robertson-Walker line-element with flat three-space. The solution represents a cosmological model that develops into an inflationary era.     

Two fluid scenario for dark energy model in Brans-Dicke theory of gravitation

In this paper, we study the evolution of the dark energy parameter in the spatially homogeneous and isotropic Friedmann-Robertson-Walker (FRW) model filled with barotropic fluid and dark energy in the scalar-tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 24:925, 1961). A determinate solution is presented using (i) the special law of variation for Hubble’s parameter proposed by Berman (Nuovo Cimento B 74:183, 1983) and (ii) trace free energy momentum tensor of the two fluid. Two cases of interacting and non-interacting fluid (barotropic and dark energy) scenario is considered and general results are obtained. The physical aspects of the results obtained are, also, discussed.     

Plane symmetric vacuum bianchi type I cosmological model in Brans-Dicke theory

The paper presents an exact solution of the vacuum Brans-Dicke field equations for the metric tensor of a spatially homogeneous and anisotropic cosmological model. The Kasner metric is shown as a special case. Some physical properties of the model are discussed.     

A higher-dimensional string cosmological model in Brans–Dicke theory of gravitation

Field equations in the presence of cosmic string source are obtained in a scalar tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124, 925 (1961)) with the aid of a five-dimensional Kaluza–Klein metric. An exact string cosmological model is presented which represents a five-dimensional Reddy string (Astrophys. Space Sci. 286, 2003b) in Brans–Dicke theory. Some physical properties of the model are also discussed