Slowly rotating cosmological perfect fluids in Brans-Dicke theory

The Brans-Dicke field equations for a perfect fluid distribution representing slowly rotating fluid spheres are investigated. Exact solutions are obtained for differential rotation and perfect dragging by imposing some physical restrictions on the matter rotation (r,t). The physical properties are discussed fork=±1.     

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.     

Non-static conformally flat spherically symmetric perfect fluid distribution in Einstein-Cartan theory

In this paper we have obtained general solution representing conformally-flat, non-static spherically-symmetric perfect fluid distribution in Einstein-Cartan theory. In particular, the solution has been also discussed in co-moving coordinates. The explicit expressions for pressure, density, expansion, rotation, shear and non-vanishing components of flow vector have also been found.     

Slowly rotating cosmological viscous fluid universe in Brans-Dicke theory

The Brans-Dicke field equations for a viscous distribution representing slowly rotating fluid spheres are investigated. Exact solutions are obtained for differential rotation by imposing physical restrictions on the matter rotation (r,t). The physical properties are discussed fork=±1.     

Gravitational charged perfect fluid collapse in Friedmann universe models

This paper is devoted to the study of gravitational charged perfect fluid collapse in Friedmann universe models with cosmological constant. For this purpose, we assume that the electromagnetic field is so weak that it does not introduce any distortion into the geometry of the spacetime. The results obtained from the junction conditions between the Friedmann and the Reissner–Nordström de Sitter spacetimes are used to solve the field equations. Further, the singularity structure and mass effects of the collapsing system on the time difference between the formation of apparent horizons and singularity have been studied. This analysis provides the validity of the Cosmic Censorship Hypothesis. It is found that the electromagnetic field affects the area of apparent horizons and their time of formation.     

Equilibrium of a static charged perfect fluid sphere

A study is developed for treating Einstein-Maxwell's equations, applied to a static perfect fluid sphere with charge, in a such a manner to generalize the Oppenheimer and Volkoff hydrostatic equilibrium equation.We suggest reasons which could make the generalization of this equation inapplicable. It is shown that Einstein-Maxwell's equations predict such special solutions.     

Electromagnetic mass model of a static charged perfect fluid sphere

Using the results, which they have been already published in two earlier papers (Dionysiou, 1982; Dionysiou and Kostakis, 1983; these papers will hereafter be referred to as Papers I, II, respectively), one can easily see that the total gravitational mass, the density and pressure of a static charged perfect fluid sphere are of electromagnetic origin.     

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.     

Solutions of Einstein-Maxwell field equations for a static charged perfect fluid shphere

The object of this paper is to give a new mathematical and physical method of finding explicit analytical interior solutions of the Einstein-Maxwell field equations of a static perfect fluid sphere with charge. In spite of many successful efforts in solving the field equations, the importance of finding meaningful general analytic solutions remains. Our purpose is to obtain the interior solutions of the field equations that they complete the results, which they have been already published in an earlier paper (Dionysiou, 1982; this paper will be referred to hereafter as Paper I). Using our new formulae, we then rederive some known results as particular solutions.     

Density perturbations in the Brans-Dicke theory

We give here the calculation of density perturbations in a gravitation theory with a scalar field non-minimally coupled to gravity, i.e., the Brans-Dicke theory of gravitation. The purpose is to show the influence of this scalar field on the dynamic behaviour of density perturbations along the eras where the equation of state for the matter can be put under the formp=, where is a constant. We analyse the asymptotic behaviour of this perturbations for the cases =0, =–1, =1/3 and =0. In general, we obtain a decaying and growing modes. In the very important case of inflation, =–1, there is no density perturbation, as it is well known. In the vacuum phase the perturbations on the scalar field and the gravitational field present growing modes at the beginning of the expansion and decaying modes at the end of this phase. In the case =0 it is possible, for some negative values of , to have an amplification of the perturbations with a superluminal expansion of the scale factor. We can also obtain strong growing modes for the density contrast for the case where there is a contraction phase which can have physical interest in some primordial era.     

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.     

Bianchi type I cosmological perfect fluid model in scale invariant theory

The intention of this paper is to study the perfect fluid distribution in scale invariant theory of gravity when the space-time is described by Bianchi type I metric with a time dependent gauge function. The cosmological equations for this space-time with gauge function are solved and some physical properties of the model are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

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 study of Brans-Dicke theory in FRW-model

In FRW space time Brans-Dicke theory is developed for two cases: (i) the vacuum and (ii) the perfect fluid model. The field equations are transformed into a much simpler form under a change of time co-ordinates and then the solutions are determined for the above cases. An equation of statep =/3 (radiation) is assumed in the case of perfect fluid.     

The general class of Bianchi cosmological models with viscous fluid and particle creation in Brans-Dicke theory

This paper deals with the general class of Bianchi cosmological models with bulk viscosity and particle creation described by full causal thermodynamics in Brans-Dicke theory. We discuss three types of average scale-factor solutions for the general class of Bianchi cosmological models by using a special law for the deceler- ation parameter which is linear in time with a negative slope. The exact solutions to the corresponding field equations are obtained in quadrature form and solutions to the Einstein field equations are obtained for three different physically viable cosmologies. All the physical parameters are calculated and discussed in each model.     

The general dust solutions in the Brans-Dicke theory

We discuss the Brans-Dicke field equations for the non-flat (k ²=1) Friedmann-Robertson-Walker models filled with dust. It is shown that the problem of constructing the general dust solutions can be reduced to the problem of solving a first-order differential equation.     

Cosmological solution in Brans-Dicke theory involving particle creation

By considering the Robertson-Walker line element exact cosmological solutions have been obtained by taking spin-half-generated particles as matter sources in the Jordan-Brans-Dicke theory. There exist exact solutions for which the gravitational constant decreases linearly with time and the mass of the Universe increases proportionally to the square of its age while the density decreases with time. The results have been studied corresponding to the three values of curvature index. It has been shown that the expansion law is determined by the particles created by the expansion itself.     

Qualitative analysis of cosmological models in Brans-Dicke theory

Isotropic and homogeneous cosmological models with a perfect fluid cource in Brans-Dicke theory are investigated from the point of view of dynamical system theory.Work partially supported by CNPq (Brazil).