共查询到20条相似文献，搜索用时 31 毫秒
1.
《天文和天体物理学研究(英文版)》2016,(4)
On studying some new models of Robertson-Walker universes with a Brans-Dicke scalar field, it is found that most of these universes contain a dark energy like fluid which confirms the present scenario of the expansion of the universe. In one of the cases, the exact solution of the field equations gives a universe with a false vacuum, while in another it reduces to that of dust distribution in the Brans-Dicke cosmology when the cosmological constant is not in the picture. In one particular model it is found that the universe may undergo a Big Rip in the future, and thus it will be very interesting to investigate such models further. 相似文献
2.
R. Chaubey 《Astrophysics and Space Science》2012,342(2):499-509
The Bianchi type-V cosmological model with viscous fluid and creation particle in Brans-Dicke theory has been considered. The present paper deals with Bianchi type-V cosmological model with bulk viscosity and particle creation described by full causal thermodynamics in Brans-Dicke theory. We have discussed two types of solutions of the average scale factor for a Bianchi type-V model by using a variation law of Hubble’s parameter, which yields a constant value of the deceleration parameter. The exact solutions to the corresponding field equations are obtained in quadrature form. The solutions to the Einstein field equations are obtained for power law and exponential form. The cosmological parameters have been discussed in detail. 相似文献
3.
Raychaudhuri-type equations are derived for cosmological models filled with a perfect fluid and obeying the Brans-Dicke equations with a cosmological term depending on the scalar field. In addition, some general results on spatially homogeneous cosmological models are obtained in the theories due to Bergmann and Wagoner and Uehara and Kim. 相似文献
4.
This paper deals with the study of dynamical or phase space analysis of Bianchi I universe in Brans-Dicke gravity with chameleon scalar field. For this purpose, the matter contents are taken to be perfect fluid with magnetic field effects described by the non-linear Maxwell Lagrangian density. By taking some ansatz for the field potential and the interaction function in chameleon cosmology, we discuss three cases: Bianchi I universe with perfect fluid, FRW universe with magnetized perfect fluid and Bianchi I universe with magnetized perfect fluid. In all cases, we calculate fixed or critical points and discuss stability of the respective configuration for radiation as well as matter dominated eras. We also evaluate some cosmological parameters in each case for matter dominated era only and investigate their cosmological implications. 相似文献
5.
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. 相似文献
6.
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. 相似文献
7.
Shri Ram 《Astrophysics and Space Science》1983,94(2):307-310
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. 相似文献
8.
Marcelo Samuel Berman 《Astrophysics and Space Science》2008,314(1-3):79-82
A combined BCDE (Brans-Dicke and Einstein-Cartan) theory with lambda-term is developed through Raychaudhuri’s equation, for
inflationary scenario. It involves a variable cosmological constant, which decreases with time, jointly with energy density,
cosmic pressure, shear, vorticity, and Hubble’s parameter, while the scale factor, total spin and scalar field increase exponentially.
The post-inflationary fluid resembles a perfect one, though total spin grows, but the angular speed does not (Astrophys. Space
Sci. 312: 275, 2007d).
相似文献
9.
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). 相似文献
10.
Shri Ram 《Astrophysics and Space Science》1987,133(2):397-401
An algorithm is derived for constructing spatially-homogeneous perfect fluid solutions of Einstein's field equations which are of Bianchi type-I and are locally rotationally-symmetric. Starting from Bayin and Krisch solution a new exact solution is obtained. Some physical and kinematic properties of the cosmological model are discussed. 相似文献
11.
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. 相似文献
12.
Homogenous isotropic cosmologies in the presence of a cosmological constant A are studied in the modified Brans-Dicke theory.
A class of exact solutions are obtained in Dicke's revised units for empty space as well as for the models filled with dust
or radiation. Behaviour of these models near the singularity are discussed. 相似文献
13.
Relativistic cosmological field equations are obtained for a non-static stationary Bertotti-Robinson-type space-time for interacting perfect fluid and electromagnetic field. The cosmological solution to the field equations are obtained and the nature of the electromagnetic field as well the perfect fluid are studied. The electromagnetic field generated here corresponds to a special generic case and the perfect fluid distribution degenerates into a barotropic perfect fluid with equation of statep+=0, >0. It is shown here that the interacting barotropic fluid can generate gravitation only when the cosmological constant being a function ofx in a dynamic field. 相似文献
14.
Some cylindrically symmetric inhomogeneous cosmological models for perfect fluid distributions with electromagnetic field
are obtained. To get a determinate solution, a supplementary condition between metric potentials is used. Various physical
and geometrical properties of the models with some special cases are also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
An exact Bianchi type-I cosmological model in the presence of zero-mass scalar fields is obtained when the source of the gravitational field is a perfect fluid with pressure equal to energy density. Some properties of the model are discussed. 相似文献
16.
We present an exact solution of the Brans-Dicke equations for cosmological models of Bianchi type VI0 with stiff matter. The solution represents anisotropic universe which has its analogy in Einstein's theory. The corresponding result for a plane symmetry Bianchi type I model is obtained as a special case. 相似文献
17.
An exact Bianchi type-III cosmological model in the presence of zero-mass scalar fields is obtained when the source of the gravitational field is a perfect fluid with pressure equal to energy density. Some properties of the model are also discussed. 相似文献
18.
In this paper we have taken an attempt to construct a five dimensional perfect fluid cosmological model within the framework
of Lyra manifold. It is found that neither perfect fluid nor dust distributions survive. Finally the exact solutions of the
vacuum field equations are obtained. 相似文献
19.
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. 相似文献
20.
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. 相似文献