共查询到20条相似文献，搜索用时 15 毫秒
1.
G. Mukherjee 《Journal of Astrophysics and Astronomy》1983,4(4):295-300
The Bianchi type I cosmological models have been extensively studied in the past especially as examples of the homogeneous shearing universe. This paper presents a tilted universe solution admitting this group of motion where the velocity field is shear-free but there is an energy flux term. 相似文献
2.
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
3.
Power-law solutions for f(G) gravity coupled with perfect fluid have been studied for spatially flat universe. It is shown that despite the matter dominated
and accelerating power-law solutions, the power-law solution exists for an special form of f(G) when this universe enters a Phantom phase. 相似文献
4.
We consider a spatially homogeneous and isotropic flat Robertson-Walker model filled with a scalar (or tachyonic) field minimally
coupled to gravity in the framework of higher derivative theory. We discuss the possibility of the emergent universe with
normal and phantom scalar fields (or normal and phantom tachynoic fields) in higher derivative theory. We find the exact solution
of field equations in normal and phantom scalar fields and observe that the emergent universe is not possible in normal scalar
field as the kinetic term is negative. However, the emergent universe exists in phantom scalar field in which the model has
no time-like singularity at infinite past. The model evolves into an inflationary stage and finally admits an accelerating
phase at late time. The equation of state parameter is found to be less than −1 in early time and tends to −1 in late time
of the evolution. The scalar potential increases from zero at infinite past to a flat potential in late time. More precisely,
we discuss the particular case for phantom field in detail. We also carry out a similar analysis in case of normal and phantom
tachyonic field and observe that only phantom tachyonic field solution represents an emergent universe. We find that the coupling
parameter of higher order correction affects the evolution of the emergent universe. The stability of solutions and their
physical behaviors are discussed in detail. 相似文献
5.
D. R. K. Reddy 《Astrophysics and Space Science》1986,122(2):263-265
The exterior field of the Robertson-Walker type metric in the Lyttleton-Bondi universe is considered and an exact solution is obtained. Some physical properties of the solution are discussed. 相似文献
6.
A new class of exact solutions of Einstein's field equations with perfect fluid for an LRS Bianchi type-I spacetime is obtained by using a time dependent deceleration parameter. We have obtained a general solution of the field equations from which three models of the universe are derived: exponential, polynomial and sinusoidal form respectively. The behaviour of these models of the universe are also discussed in the frame of reference of recent supernovae Ia observations. 相似文献
7.
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
8.
A new solution of Einstein-Maxwell field equations is presented. The material content of the field described by this solution
is a perfect fluid plus sourceless electromagnetic fields. The metric of the solution is explicitly written. This metric is
examined as a possible representation of Kerr-Newman metric embedded in Einstein static universe. The Kerr-Newman metric in
the background of Robertson-Walker universe is also briefly described. 相似文献
9.
The exact solution is sought for the cosmological equations of Brans and Dicke's scalar-tensor theory when a power law exists between the gravitational constant and the radius of curvature of the universe. For the space of negative curvature no solution is possible. On the contrary for a closed space the gravitational constant and the radius of curvature increase linearly with respect to the age of the universe. The parameter of the scalar-tensor theory is necessarily negative and can be determined by the present values of the mass-density of the universe, the Hubble-constant and the gravitational constant. The solution has no analogy in Einstein's theory with vanishing cosmological constant, even when the deviations from Einstein's values of the solar relativistic effects are small. 相似文献
10.
J. V. Narlikar 《Journal of Astrophysics and Astronomy》1984,5(1):67-78
The concept of the steady-state universe discussed by Hoyle & Narlikar two decades ago is revived in the light of the present
discussions of the phase transition in the early big-bang universe. It is shown that with suitable scaling the bubble universe
solution bears a striking similarity to the inflationary scenarios being discussed today. The currently discussed idea of
cosmic baldness was also anticipated in the C-field cosmology of the steady-state universe.
An erratum to this article is available at . 相似文献
11.
A. Bhadra 《Astrophysics and Space Science》2007,310(1-2):169-172
Scalar tensor (ST) theories of gravitation contain an attractor mechanism towards general relativity. The mechanism is supposed
to start back at time of inflation. Consequently the characteristic coupling function of the ST theories could attain a very
large value during the radiation epoch. Here ST cosmology in the radiation dominated universe is studied under such situation.
A general solution of the scale factor in the radiation dominated flat universe is obtained that is characterized by an additional
degree of freedom. An implication of this extra parameter is discussed.
相似文献
12.
Sanjay Sarkar 《Astrophysics and Space Science》2014,352(2):859-866
The present work deals with the accretion of two minimally interacting fluids: dark matter and a hypothetical isotropic fluid as the holographic dark energy components onto black hole and wormhole in a spatially homogeneous and anisotropic Bianchi type-V universe. To obtain an exact solution of the Einstein’s field equations, we use the assumption of linearly varying deceleration parameter. Solution describes effectively the actual acceleration and indicates a big rip type future singularity of the universe. We have studied the evolution of the mass of black hole and the wormhole embedded in this anisotropic universe in order to reproduce a stable universe protected against future-time singularity. It is observed that the accretion of these dark components leads to a gradual decrease and increase of black hole and wormhole mass respectively. Finally, we have found that contrary to our previous case (Sarkar in Astrophys. Space. Sci. 341:651, 2014a), the big rip singularity of the universe with a divergent Hubble parameter of this dark energy model may be avoided by a big trip. 相似文献
13.
In this work we review briefly the origin and history of the cosmological constant and its recent reincarnation in the form of the dark energy component of the universe. We also comment on the fundamental problems associated to its existence and magnitude which require an urgent solution for the sake of the internal consistency of theoretical physics. 相似文献
14.
15.
In this work we investigate the background dynamics when dark energy is coupled to dark matter with a suitable interaction
in the universe described by brane cosmology. Here DGP and the RSII brane models have been considered separately. Dark energy
in the form of modified Chaplygin gas is considered. A suitable interaction between dark energy and dark matter is considered
in order to at least alleviate (if not solve) the cosmic coincidence problem. The dynamical system of equations is solved
numerically and a stable scaling solution is obtained. A significant attempt towards the solution of the cosmic coincidence
problem is taken. The statefinder parameters are also calculated to classify the dark energy models. Graphs and phase diagrams
are drawn to study the variations of these parameters. It is also seen that the background dynamics of modified Chaplygin
gas is completely consistent with the notion of an accelerated expansion in the late universe. Finally, it has been shown
that the universe in both the models follows the power law form of expansion around the critical point, which is consistent
with the known results. 相似文献
16.
A method based on the invariace under a continuous Lie group of transformations is worked out to reduce the problem of finding solutions to the cosmological equations of Jordan and Brans-Dicke theory of gravitation for the Robertson-Walker metrics and the cases of the dust universe and the vacuum universe. The reduction consists in a first-order differential equation and a quadrature for each case. Previously known cosmological solutions are re-obtained. In particular, it becomes apparent during the development of this scheme that the flat-space solutions are indeed the general solution. 相似文献
17.
The bounce with non-minimal coupling is very interesting topic because in the early time, general relativity is likely to
be modified, which can give some valuable effects to the evolution of our universe. In this paper we introduce a string-inspired
model for bouncing universe, utilizing the tachyon field as well as contributions from general non-minimal kinetic couplings
and curvature. It is shown numerically that the bouncing solution appears in the model whereas the equation of state (EoS)
parameter crosses the phantom divider. 相似文献
18.
The exterior field of the Robertson-Walker-type metric in the Lyttleton-Bondi universe is studied and exact solutions are obtained for closed and open universes. Only the flat space solution was previously known. 相似文献
19.
《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
20.
Sanjay Sarkar 《Astrophysics and Space Science》2014,350(2):821-829
In this work, we have considered the spatially homogeneous and anisotropic Bianchi type-II universe filled with two interacting fluids; dark matter and holographic dark energy components. Assuming the proportionality relation between one of the components of shear scalar and expansion scalar which yields time dependent deceleration parameter, an exact solution to Einstein’s field equations in Bianchi type-II line element is obtained. We have investigated geometric and kinematics properties of the model and the behaviour of the holographic dark energy. It is observed that the mean anisotropic parameter is uniform through the whole evolution of the universe and the coincidence parameter increases with increasing time. The solutions are also found to be in good agreement with the results of recent observations. We have applied the statefinder diagnostics method to study the behaviour of different stages of the universe and to differentiate the proposed dark energy model from the ΛCDM model. We have also established a correspondence between the holographic dark energy model and the tachyon scalar field dark energy model. We have reconstructed the potential and the dynamics of the tachyon scalar field, which describes accelerated expansion of the universe. 相似文献