共查询到20条相似文献，搜索用时 46 毫秒
1.
We discuss the Bianchi type I model with perfect fluid as matter content in f(R,T) gravity, where R is the Ricci scalar and T is the trace of the energy-momentum tensor. We obtain exact solutions of the field equations employing the anisotropic feature of spacetime for two expansion laws namely exponential and power expansions. The physical and kinematical quantities are examined for both cases in future evolution of the universe. We also explore the validity of null energy condition and conclude that our solutions are consistent with the current observations. 相似文献
2.
In this paper we present a class of non-stationary solutions of Einstein’s field equations describing embedded Vaidya-de Sitter black holes with a cosmological variable function Λ(u). The Vaidya-de Sitter black hole is interpreted as the radiating Vaidya black hole is embedded into the non-stationary de Sitter space with variable Λ(u). The energy-momentum tensor of the Vaidya-de Sitter black hole is expressed as the sum of the energy-momentum tensors of the Vaidya null fluid and that of the non-stationary de Sitter field, and satisfies the energy conservation law. We study the energy conditions (like weak, strong and dominant conditions) for the energy-momentum tensor. We find the violation of the strong energy condition due to the negative pressure and leading to a repulsive gravitational force of the matter field associated with Λ(u) in the space-time. We also find that the time-like vector field for an observer in the Vaidya-de Sitter space is expanding, accelerating, shearing and non-rotating. It is also found that the space-time geometry of non-stationary Vaidya-de Sitter solution with variable Λ(u) is Petrov type D in the classification of space-times. We also find the Vaidya-de Sitter black hole radiating with a thermal temperature proportional to the surface gravity and entropy also proportional to the area of the cosmological black hole horizon. 相似文献
3.
Time-dependent wormhole solutions are found which evolve on inhomogeneous spherically symmetric space time. By using a constraint
on energy-momentum tensor, solutions are derived from Einstein’s equations with cosmological constant. 相似文献
4.
Gamal G. L. Nashed 《Astrophysics and Space Science》2011,333(1):317-325
We derive three different solutions in the framework of the teleparallel equivalent of general relativity (TEGR). We apply
the energy-momentum tensor to calculate energy, irreducible mass, spatial momentum and angular-momentum associated with these
solutions. We obtain anomalous physical results therefore, we calculate the Killing vectors using the definition of the Lie
derivative. 相似文献
5.
Ngangbam Ishwarchandra N. Ibohal K. Yugindro Singh 《Astrophysics and Space Science》2014,353(2):633-639
In this paper we present an exact solution of Einstein’s field equations describing the Schwarzschild black hole in dark energy background. It is also regarded as an embedded solution that the Schwarzschild black hole is embedded into the dark energy space producing Schwarzschild-dark energy black hole. It is found that the space-time geometry of Schwarzschild-dark energy solution is non-vacuum Petrov type D in the classification of space-times. We study the energy conditions (like weak, strong and dominant conditions) for the energy-momentum tensor of the Schwarzschild-dark energy solution. We also find that the energy-momentum tensor of the Schwarzschild-dark energy solution violates the strong energy condition due to the negative pressure leading to a repulsive gravitational force of the matter field in the space-time. It is shown that the time-like vector field for an observer in the Schwarzschild-dark energy space is expanding, accelerating, shearing and non-rotating. We investigate the surface gravity and the area of the horizons for the Schwarzschild-dark energy black hole. 相似文献
6.
Conformally-invariant scalar field with trace-free energy-momentum tensor in Robertson-Walker models
Exact solutions of Einstein's field equations for a conformally-invariant scalar field with trace-free energy-momentum tensor is presented for the Robertson-Walker models withK=+1, –1. The physical properties of the solution are also studied. 相似文献
7.
Gamal G. L. Nashed 《Astrophysics and Space Science》2010,330(1):173-181
We apply the energy-momentum tensor which is coordinate independent to calculate the energy content of the axisymmetric solutions.
Our results are compared with what have been obtained before within the framework of Einstein general relativity and M?ller’s
tetrad theory of gravitation. 相似文献
8.
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
9.
N. Riazi 《Astrophysics and Space Science》2003,283(2):235-244
Spherical, time-dependent geometrical structures in an inflationary RW background are derived from the Einstein equations,
using a constraint on the energy-momentum tensor which is an extension of the one expected for inflation. The possibility
of dynamical wormholes and other spherical structures are explored in the framework of the solutions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
Time-dependent wormhole solutions are found which evolve in a cosmological background. Solutions are presented both for GR
and Brans-Dicke field equations. Conditions are derived for the supporting matter to be non-exotic. The traceless energy-momentum
tensor needed to support the geometry is in the form of an anisotropic fluid. Far from the wormhole, the equation of state
rapidly approaches that of an isotropic perfect fluid with p = 1/3 ρ. For the BD wormholes we obtain ρ = 0everywhere, except for the π = const. limit, in which case the GR results are
reproduced.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
We study Bianchi type I cosmological model in the presence of magnetized anisotropic dark energy. The energy-momentum tensor consists of anisotropic fluid with anisotropic EoS p=ω ρ and a uniform magnetic field of energy density ρ B . We obtain exact solutions to the field equations using the condition that expansion is proportional to the shear scalar. The physical behavior of the model is discussed with and without magnetic field. We conclude that universe model as well as anisotropic fluid do not approach isotropy through the evolution of the universe. 相似文献
12.
Recently, Innaiah and Reddy (1985) obtained a flat Robertson-Walker-type solution for the Einstein field equations with the trace-free energy-momentum tensor of a conformally invariant scalar field as source. Here we show that the field equations force the scalar field to be independent of time. Furthermore, we obtain open and closed Robertson-Walker-type solutions and observe that, once again, the scalar field has to be independent of time. 相似文献
13.
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
14.
We consider a generalization of the Standard Model whose action displays conformal invariance in d dimensions. The model contains a strongly coupled dark matter sector which breaks conformal symmetry dynamically. The model evades conformal anomaly and leads to identically zero vacuum energy in flat space-time. Hence it does not suffer from the problem of fine tuning of the cosmological constant. We determine the contribution of non-relativistic matter to the energy-momentum tensor and determine a parameter regime in which it approximately reduces to the standard result. We show how dark energy and dark matter arises in this model. We discuss the parameter range for which the model reduces to the ΛCDM model and hence is consistent with observations. 相似文献
15.
In this paper, we have investigated Bianchi type VI h cosmological model filled with perfect fluid in the framework of f(R,T) gravity, where R is the Ricci scalar and T is the trace of the energy-momentum tensor proposed by Harko et al. (Phys. Rev. D 84:024020, 2011). We have obtained the cosmological models by solving the field equations. Some physical behaviors of the model are also studied. 相似文献
16.
Farook Rahaman 《Astrophysics and Space Science》2002,282(4):625-633
Thick domain walls with time dependent displacement vector based on Lyra's geometry are considered. Their exact solutions are obtained in the background of a five-dimensional space time. The field theoretic energy-momentum tensor is considered assuming with $$T_t^t = T_x^x = T_y^y = T_\psi ^\psi .$$ Acceleration due to the domain wall has been evaluated by studyinggeodesic equation. 相似文献
17.
Exact solutions are obtained in a five-dimensional space-time with an energy-momentum tensor containing a viscous fluid, assuming either an equation of state or a special form for the viscous term in line with the assumption of Belinskii and Khalatnikov (1977). The solutions are, in fact, generalizations of an earlier work by Grøn for a perfect fluid in the 5D rest-mass varying theory of gravity proposed recently by Wesson. It is found that dimensional reduction of the extra space takes place in some of the cases such that the 5-dimensional universe naturally evolves into an effective 4-dimensional one. A huge amount of entropy can be produced following this shrinkage of extra-dimension which may account for the very large value of entropy per baryon observed in our 4D world. Moreover, the observed constancy of the rest-mass in the present era is also interpreted. 相似文献
18.
Metod Saniga 《Astrophysics and Space Science》1993,207(2):301-304
Several authors have studied solutions of Einstein's field equations for a conformally invariant scalar field with trace-free energy-momentum tensor for the Robertson-Walker models forK = 0, ± 1. The relationship of these solutions to a previously existing one by Som (1985) is discussed. TheK = 0 model derived by Innaiah and Reddy (1985) is shown to be a special case of the Bianchi type-I models due to Accioly, Vaidya and Som (1983a). 相似文献
19.
R. Illge 《Astronomische Nachrichten》1988,309(4):253-257
20.
We discuss spatially homogeneous and anisotropic Bianchi type VI
0 cosmological model with anisotropic fluid and magnetic field. The energy-momentum tensor consists of anisotropic fluid with
anisotropic EoS and a uniform magnetic field of energy density ρ
B
. Exact solution of the field equations is obtained by using the condition that expansion is proportional to the shear scalar.
We focus on the future evolution of the model both in the presence and absence of magnetic field. In particular, we address
the question whether these models approach to isotropy. 相似文献