共查询到20条相似文献,搜索用时 9 毫秒
1.
The imposition of boundary conditions on the background fields of brane-world models leads to nonzero vacuum averages for the corresponding energy-momentum tensor. Methods from the qualitative theory of dynamic systems are used in this paper to study the cosmological evolution generated by this tensor. All the possible types of cosmological dynamics are examined for models with homogeneous and isotropic subspaces on the branes and the behavior of the corresponding solutions is studied in the early and late stages of evolution. 相似文献
2.
3.
Han Ji-chang 《Chinese Astronomy and Astrophysics》1981,5(3):357-364
For the Robertson-Walker metric for a homogeneous and isotropic universe, I have derived explicit solutions of the Einstein-Yang equation (interior torsion-free solutions for a spin-less ideal fluid) and hence found certain solutions of the Einstein field equation for the radiation-dominated phase of the early universe. 相似文献
4.
S. Gottl
ber 《Astronomische Nachrichten》1984,305(1):1-4
The behaviour of classical massive scalar and vector fields as sources of homogeneous world models is examined. The consequence of the violation of the strong energy condition by the massive scalar field for the evolution of an cosmological model is discussed. 相似文献
5.
Can Battal Kılınç 《Astrophysics and Space Science》2004,289(1-2):103-109
Einstein's equations with variable gravitational and cosmological constants are considered in the presence of a perfect fluid for the anizotropic Bianchi I universe in a way which conserving the energy-momentum tensor. Two solutions are found, one of which the cosmological term varies inversely with power law of time. The other of which cosmological term is constant. 相似文献
6.
In this paper we present a class of solutions of Einstein's field equations describing two-fluid models of the universe in
a locally rotationally symmetric Bianchi type II space-time. In these models one fluid is the radiation distribution which
represents the cosmic microwave background and the other fluid is the perfect fluid representing the matter content of the
universe. It is found that both the fluids are comoving in the locally rotationally symmetric Bianchi type II space-time.
The behaviour of the radiation density, matter density, the ratio of the matter density to the radiation density and the pressure
has been discussed. A subclass of solutions is found to describe models of a spatially homogeneous and partially isotropic
universe evolving from a radiation dominated era to a pressure free matter dominated era.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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8.
Field equations in a scalar-tensor theory of gravitation proposed by Saezand Ballester (1985) are obtained with the aid of
(i) Friedmann-type metric (ii) a non static plane symmetric metric and (iii) spatially homogeneous Bianchi type – III metric.
Some cosmological models corresponding to perfect fluid and bulk viscous fluid are presented. Physical and kinematical properties
of the models are also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
In this paper, the Einstein field equations have been solved for cylindrically symmetric and inhomogeneous cosmological models with viscous fluid. Various physical and geometrical properties of the models are also discussed. 相似文献
10.
The motivation of this paper is to investigate two viscous fluid cosmological models in General Relativity in which the expansion
is only in two directions i.e. one of the Hubble parameters
is zero. In the first model, coefficient of shear viscosity is assumed to be constant while in the second model, the coefficient
of shear viscosity is proportional to the rate of expansion in the model. Here no additional condition is assumed except for
coefficient of shear viscosity. These models are new and different from those models obtained by Bali and Jain (1987, 1988)
in which free gravitational field was assumed to be Petrov Type D and non-degenerate for Marder (1958) metric and coefficient
of shear viscosity is proportional to the rate of expansion in the model. The various physical and geometrical aspects of
the models are also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
The field equations of Barber's (1982) second self-creation theory of gravitation are solved for 5D Friedmann-Robertson-Walker
space time using perfect fluid energy momentum tensor. By assuming an equation of state p= ε ρ, (0 ≤ ε ≤ 1), the solutions of the field equations, in different scenarios, in Barber's second self-creation theory
are presented and discussed. Some properties of these models are also discussed. 相似文献
12.
Totally anisotropic Bianchi type-II cosmological solutions are presented in Barber's second self-creation theory of gravitation
both in vacuum and in the presence of stiff-matter. The corresponding cosmological models have no finite singularity. The
stiff-matter model gives essentially an empty universe for large time. Some physical and kinematical properties of the models
are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
Can Battal Kilinç 《Astrophysics and Space Science》2006,301(1-4):83-88
We consider Einstein's equations with variable cosmological constant in the presence of a perfect fluid for the inhomogeneous
cylindrically-symmetric space–time. We find two solutions under this conditions and analyze our solutions with respect to
the constants. 相似文献
14.
Evolution of a homogeneous, isotropic Universe with flat geometry filled with a viscous fluid is investigated in presence
of a variable cosmological Λ. A non-singular solution leading to a variable deceleration parameter is obtained which reduces
to the solution of Murphy in the ‘no Λ limit’ and to the recent solution of Vishwakarma in the context of ‘a Machian model
of dark energy’ in the ‘no viscosity’ limit. 相似文献
15.
Some Bianchi type I viscous fluid cosmological models with a variable cosmological constant are investigated in which the
expansion is considered only in two direction i.e. one of the Hubble parameter
is zero. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density whereas the coefficient
of shear viscosity is considered as constant in first case whereas in other case it is taken as proportional to scale of expansion
in the model. The cosmological constant Λ is found to be positive and is a decreasing function of time which is supported
by results from recent supernovae Ia observations. Some physical and geometric properties of the models are also discussed. 相似文献
16.
The effect of time dependent bulk viscosity on the evolution of Friedmann models with zero curvature in Brans-Dicke theory
is studied. The solutions of the field equations with ‘gamma-law’ equation of state p = (γ-1) ρ, where γ varies continuously
as the Universe expands, are obtained by using the power-law relation φ = bR
n
, which lead to models with constant deceleration parameter. We obtain solutions for the inflationary period and radiation
dominated era of the universe. The physical properties of cosmological solutions are also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
We examine the possibility that a substantial fraction of the total energy density in a spatially flat Universe is composed
of a time-dependent and spatially inhomogeneous component whose equation-of-state differs from that of baryons, neutrinos,
dark matter, or radiation. In this lecture, we report on our investigations of the case in which the additional energy component,
dubbed "quintessence", is due to a dynamical scalar field evolving in a potential. We have computed the effects on the background
cosmological evolution, the cosmic microwave background (CMB) and mass power spectrum, finding a broad range of cosmologically
viable models. We stress three important features of the quintessence or Q-component: the time evolution of the equation-of-state;
the length-scale dependence of the speed of propagation of the fluctuations in the Q-component; and, the contribution of quintessence
fluctuations to the CMB anisotropy spectrum.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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19.
Exact solutions of the gravitational field equations for a Bianchi type I anisotropic space-time, filled with a viscous cosmological fluid obeying an equation of state of the form p = , 0 1, are obtained. We investigate both the viscous Zeldovich ( = 1) and < 1 fluid cases, with constant and time varying (proportional to the mean Hubble factor) shear and bulk viscosity coefficients. It is shown that independently of the matter content, the equation of state and the time dependence of the shear and bulk viscosity coefficients, a viscous Bianchi type I universe experiences a transition to an inflationary era. Due to dissipative processes, the mean anisotropy and the shear of the Bianchi type I universe tend very rapidly to zero. 相似文献