共查询到20条相似文献，搜索用时 46 毫秒
1.
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
2.
This paper presents a set of solutions of coupled Einstein-Maxwell equations with matter for the Levi-Civita's metric which can be interpreted as electromagnetic mass models which are extensions of the electromagnetic mass models obtained previously. It may be pointed out that electromagnetic mass models are solutions of coupled Einstein-Maxwell equations with matter where all the characteristics of matter vanish when the charge vanishes. Existence of such solution tends to confirm Lorentz's conjecture that the mass of an electron may be of purely electromagnetic origin. 相似文献
3.
N. Ibotombi Singh S. Surendra Singh S. Romaleima Devi 《Astrophysics and Space Science》2010,326(2):293-297
Field equations of cosmological models with bulk viscosity are constructed in the scale covariant theory of gravitation. A
new class of solutions for the model is found by applying a variable deceleration parameter. Some physical implications of
these solutions are briefly discussed. 相似文献
4.
Multi-dimensional cosmological models with n(n > 1) Ricci-flat spaces and a scalar field are discussed classically and with respect to canonical quantization. These models are integrable. Two classes of solutions are obtained. One class of solutions generalizes the Kasner solutions. For special additional conditions we find another solution describing extended inflation connected with a constant volume of the whole multidimensional space (steady-state). 相似文献
5.
Vacuum Friedmann-Robertson-Walker cosmological models are derived in Lyra's manifold and some properties of the solutions are discussed. In addition to the usual de Sitter universe, several new solutions are obtained. 相似文献
6.
A technique to generate new exact Bianchi type-III cosmological solutions of massive strings in the presence of magnetic field is presented. Starting from Tikekar and Patel's strings models in the absence and presence of the magnetic field, new solutions are obtained. Some of their physical features are discussed. 相似文献
7.
D. Lorenz-Petzold 《Astrophysics and Space Science》1988,150(1):17-29
We investigate the perfect fluid field equations of the Bianchi-Kantowski-Sachs models on the basis ofN=1 no-scale supergravity. A wide class of non-singular solutions is given in the stiff matter as well as in the radiation-dominated case. The vacuum solutions are included as special cases. The solutions given are of much interest in connection with the low-energy approximation of superstrings. 相似文献
8.
A procedure to generate new exact solutions to Einstein equations for perfect fluids is applied to LRS Bianchi type I line-element. Starting from some known solutions a class of new perfect fluid solutions of Bianchi type I are presented. The physical and kinematical properties of spatially homogeneous and anisotropic cosmological models are studied. 相似文献
9.
Harald H. Soleng 《Astrophysics and Space Science》1987,134(2):405-406
In a recent Letter to the Editor, Beesham (1986) has claimed that the models based on the Lyra manifold allow a wider class of solutions of the vacuum field equations than models based on a Riemannian manifold. It was also argued that the cosmological term is introduced in an arbitraryad hoc fashion in general relativity.In this note I will show that all the vacuum solutions found by Beesham, can equally well be solutions of the Friedmann equations of vacuum with a cosmological term. All these solutions are well known. 相似文献
10.
In this paper we have studied the anisotropic and homogeneous Bianchi type-I universe filled with interacting Dark matter and Holographic dark energy. Here we discussed two models, in first model the solutions of the field equations are obtained for constant value of deceleration parameter where as in the second model the solutions of the field equations are obtained for special form of deceleration parameter. It is shown that for suitable choice of interaction between dark matter and holographic dark energy there is no coincidence problem (unlike ΛCDM). Also, in all the resulting models the anisotropy of expansion dies out very quickly and attains isotropy after some finite time. The Statefinder diagnostic is applied to both the models in order to distinguish between our dark energy models with other existing dark energy models. The physical and geometrical aspects of the models are also discussed. 相似文献
11.
Jin Wang 《Astrophysics and Space Science》1992,189(1):5-9
In this paper we examine models of ten-dimensional supergravity and monoples. Wormhole solutions are obtained under the Freund-Rubin-type spontaneous compactification. The meaning of the solutions is discussed in terms of the tunnelling process. 相似文献
12.
The vacuum Friedmann-Robertson-Walker (FRW) models are investigated in Dunn's theory of gravitation with extra dimensions and some properties of the solutions are discussed. 相似文献
13.
Vacuumk=0 Friedmann-type solutions in the continuous creation theory of gravitation proposed by Barber have recently been found by Reddy (1987). Here we obtain thek=±1 Friedmann solutions in Barber's theory. Also, we show that these models are, in fact, vacuum Brans-Dicke solutions that have been studied earlier by Lorenz-Petzold (1984). 相似文献
14.
Salah Haggag 《Astrophysics and Space Science》1995,225(1):137-149
Einstein field equations for a static and spherically symmetric perfect fluid are considered. A formulation given by Patiño and Rago is used to obtain a class of nine solutions, two of them are Tolman solutions I, IV and the remaining seven are new. The solutions are the correct ones corresponding to expressions derived by Patiño and Rago which have been shown by Knutsen to be incorrect. Similar to Tolman solution IV each of the new solutions satisfies energy conditions inside a sphere in some range of two independent parameters. Besides, each solution could be matched to the exterior Schwarzschild solution at a boundary where the pressure vanishes and thus the solutions constitute a class of new physically reasonable stellar models. 相似文献
15.
We analyze the flow of a perfect relativistic fluid in a confining channel of variable cross-section — a situation that is relevant for models of radio galaxies. Families of soliton-like solutions are found and their topologies described. However, a perturbative investigation of these solutions indicates that all such soliton modes are unstable, and would eventually decay. 相似文献
16.
Harald H. Soleng 《Astrophysics and Space Science》1987,137(2):373-384
Two exact solutions of Einstein's field equations of vacuum are presented and investigated. We will regard the term vacuum fluid as the limiting case of scalar field with an almost constant potential. Considering the four velocity of this fluid we find, that in both solutions there is an anisotropic expansion of the cosmic fluid, but the fluid has vanishing vorticity.We investigate whether shear could prevent the transition into an inflationary era in these models, and the effect of shear on a scalar field is also considered. It is found that shear will speed up the rollover of the scalar field in some Bianchi type-VIII models.Possible initial conditions are discussed in light of the group structures of the models. 相似文献
17.
The vacuum Friedmann models are investigated in self-creation theory of gravitation proposed by Barber. New solutions are obtained forK=±1, and some properties of the solutions are discussed. Only theK=0 solution in self-creation cosmology was previously shown. 相似文献
18.
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
19.
20.
We obtain some cosmological models that are exact solutions of Einstein's field equations. The metric utilized is Marder's metric which is Bianchi Type I and the curvature source is a cloud of strings which are one dimensional objects. Bianchi type cosmological models play an important role in the study of the universe on a scale which anisotropy is not ignored. In this paper we have investigated the effect of cosmic strings on the cosmic microwave background anisotropy. Various physical and geometrical properties of the model are also discussed. The solutions have reported that the cosmic microwave background anisotropy may due to the cosmic strings. 相似文献