共查询到20条相似文献,搜索用时 937 毫秒
1.
A. A. Coley 《International Journal of Theoretical Physics》1995,34(2):293-299
Some general solutions of the (general)D-dimensional vacuum Einstein field equations are obtained. The four-dimensional properties of matter are studied by investigating whether the higher-dimensional vacuum field equations reduce (formally) to Einstein's four-dimensional theory with matter. It is found that the solutions obtained give rise to an induced four-dimensional cosmological perfect fluid with a (physically reasonable) linear equation of state. 相似文献
2.
Embeddings into higher dimensions are very important in the study of higher-dimensional theories of our Universe and in high-energy
physics. Theorems which have been developed recently guarantee the existence of embeddings of pseudo-Riemannian manifolds
into Einstein spaces and more general pseudo-Riemannian spaces. These results provide a technique that can be used to determine
solutions for such embeddings. Here we consider local isometric embeddings of four-dimensional spherically symmetric spacetimes
into five-dimensional Einstein manifolds. Difficulties in solving the five-dimensional equations for given four-dimensional
spaces motivate us to investigate embedded spaces that admit bulks of a specific type. We show that the general Schwarzschild–de
Sitter spacetime and Einstein Universe are the only spherically symmetric spacetimes that can be embedded into an Einstein
space of a particular form, and we discuss their five-dimensional solutions. 相似文献
3.
Higher Dimensional Strange Quark Matter Coupled to the String Cloud with Electromagnetic Field Admitting One Parameter Group of Conformal Motion
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
PRADHAN Anirudh KHADEKAR G.S. MISHRA Mukesh Kumar KUMBHARE Sarojt 《中国物理快报》2007,24(10):3013-3015
We solve Einstein's field equations in higher-dimensional spherically symmetric spacetime with strange quark matter attached to the string cloud, assuming one parameter group of con formal motions. The solutions match with the higher-dimensional Reissner-Nordstroem metric on the boundary at r=ro. The features of the solutions are also discussed in the framework of higher-dimensional spacetime. 相似文献
4.
In this work we present an exact solution of the Einstein–Maxwell field equations describing compact charged objects within the framework of classical general relativity. Our model is constructed by embedding a four-dimensional spherically symmetric static metric into a five-dimensional flat metric. The source term for the matter field is composed of a perfect fluid distribution with charge. We show that our model obeys all the physical requirements and stability conditions necessary for a realistic stellar model. Our theoretical model approximates observations of neutron stars and pulsars to a very good degree of accuracy. 相似文献
5.
Kornel Lanczos 《General Relativity and Gravitation》1997,29(3):363-399
A world is to be considered stationary in the sense of general relativity if the coefficients of its metric are independent of time in a coordinate system in which the masses are at rest on average. The remark on the system of coordinates is important because time itself is no invariant notion but is taken only in the sense of proper time. Our definition is unique, in the form given above. On the other hand it is also possible to have points where no matter is present. At such points we may place a test body of infinitesimally small mass and analyse whether it remains at rest in our coordinate system. A necessary and sufficient condition for this is that the time lines of our coordinate system are geodesics. Therefore the static solution given by de Sitter is not an example of a stationary world. The Schwarzschild line element which, from a cosmological point of view, is a world with a single central body can also not be considered a stationary solution. Indeed, there are no stationary solutions which are also spherically symmetric for the original field equations. The only such solution for the cosmological equations is Einstein's cylinder world. It is, to my knowledge, the only stationary world known so far. In that case the average matter density and the total mass of the world has to have a well defined value given by the cosmological constant which doubtless would be purely coincidental and is thus not a satisfactory assumption. In the following we shall discuss a new solution which is in accord with the original field equations without the need of an a priori relation between mass and cosmological constant. However, we shall find that its mass cannot be less than the mass of the cylinder world. 相似文献
6.
Eduard Herlt 《General Relativity and Gravitation》1983,15(12):1131-1138
The Jordan-Brans-Dicke field equations [1] contain the four-dimensional field equations of the five-dimensional projective unified theory. As it should be, Einstein's theory is incorporated as a limiting case. In this paper we present a method to determine explicitly for every static spherically symmetric solution of Einstein's theory with perfect fluid an analogous solution of Jordan-Brans-Dicke theory. As a particular example a “generalized interior Schwarzschild solution” is given. 相似文献
7.
We consider the static and spherically symmetric field equations of general relativity for charged perfect fluid spheres in
the presence of a cosmological constant. Following work by Florides (J Phys A Math Gen 16:1419–1433, 1983) we find new exact solutions of the field equations, and discuss their mass radius ratios. These solutions, for instance,
require the charged Nariai metric to be the vacuum part of the spacetime. We also find charged generalizations of the Einstein
static universe and speculate that the smallness problem of the cosmological constant might become less problematic if charge
is taken into account. 相似文献
8.
Durmu? A. Demir 《Physics letters. [Part B]》2011,701(4):496-502
We study gravitational properties of vacuum energy by erecting a geometry on the stress-energy tensor of vacuum, matter and radiation. Postulating that the gravitational effects of matter and radiation can be formulated by an appropriate modification of the spacetime connection, we obtain varied geometrodynamical equations which properly comprise the usual gravitational field equations with, however, Planck-suppressed, non-local, higher-dimensional additional terms. The prime novelty brought about by the formalism is that, the vacuum energy does act not as the cosmological constant but as the source of the gravitational constant. The formalism thus deafens the cosmological constant problem by channeling vacuum energy to gravitational constant. Nevertheless, quantum gravitational effects, if any, restore the problem via the graviton and graviton-matter loops, and the mechanism proposed here falls short of taming such contributions to cosmological constant. 相似文献
9.
Gaetano Moschetti 《General Relativity and Gravitation》1987,19(2):155-170
The problem of finding spherically symmetric self-similar solutions of Einstein's field equations with a barotropic perfect fluid, which can be joined through a shock wave to some cosmological models, is considered. It is found that such solutions comprise an expanding shell of matter surrounding a horizon with an interior singularity. 相似文献
10.
Conditions for smooth cosmological models are set out and applied to inhomogeneous spherically symmetric models constructed by matching together different Lemaître–Tolman–Bondi solutions to the Einstein field equations. As an illustration the methods are applied to a collapsing dust sphere in a curved background. This describes a region which expands and then collapses to form a black hole in an Einstein de Sitter background. We show that in all such models if there is no vacuum region then the singularity must go on accreting matter for an infinite LTB time. 相似文献
11.
In the present paper we apply Nash’s theory of perturbative geometry to the study of dark matter gravity in a higher-dimensional space–time. It is shown that the dark matter gravitational perturbations at local scale can be explained by the extrinsic curvature of the standard cosmology. In order to test our model, we use a spherically symmetric metric embedded in a five-dimensional bulk. As a result, considering a sample of 10 low surface brightness and 6 high surface brightness galaxies, we find a very good agreement with the observed rotation curves of smooth hybrid alpha-HI measurements. 相似文献
12.
We consider the recently proposed non-relativistic Ho?ava–Lifshitz four-dimensional theory of gravity. We study a particular limit of the theory which admits flat Minkowski vacuum and we discuss thoroughly the quadratic fluctuations around it. We find that there are two propagating polarizations of the metric. We then explicitly construct a spherically symmetric, asymptotically flat, black hole solution that represents the analog of the Schwarzschild solution of GR. We show that this theory has the same Newtonian and post-Newtonian limits as GR and thus, it passes the classical tests. We also consider homogeneous and isotropic cosmological solutions and we show that although the equations are identical with GR cosmology, the couplings are constrained by the observed primordial abundance of 4He. 相似文献
13.
Hongya Liu 《General Relativity and Gravitation》1991,23(7):759-765
Spherically symmetric solutions coupled to massive scalar particles in five-dimensional Kaluza-Klein theory are obtained. The solutions contain two event horizons. The inner horizon corresponds to the Schwarzschild black hole and the outer one is a new horizon which is produced by the massive scalar particles. It is found that the massive modes contribute an effective cosmological constant to the four-dimensional Einstein theory. 相似文献
14.
In this paper, we have studied a 5-dimensional warped product space-time with a time-dependent warp factor. This warp factor
plays an important role in localizing matter to the 4-dimensional hypersurface constituting the observed universe and leads
to a geometric interpretation of dynamical dark energy. The five-dimensional field equations are constructed and its solutions
are obtained. The nature of modifications produced by this warp factor in the bulk geometry is discussed. The hypersurface
is described by a flat FRW-type metric in the ordinary spatial dimension. It is found that the effective cosmological constant
of the four-dimensional universe is a variable quantity monitored by the time-dependent warp factor. The universe is initially
decelerated, but subsequently makes a transition to an accelerated phase at later times. 相似文献
15.
T. R. P. Caramês E. R. Bezerra de Mello 《The European Physical Journal C - Particles and Fields》2009,64(1):113-121
In this paper we investigate spherically symmetric vacuum solutions of f(R) gravity in a higher-dimensional spacetime. With this objective we construct a system of non-linear differential equations
whose solutions depend on the explicit form assumed for the function
F(R)=\fracdf(R)dRF(R)=\frac{df(R)}{dR}
. We explicit show that for specific classes of this function exact solutions from the field equations are obtained; also
we find approximated results for the metric tensor for more general cases admitting F(R) close to the unity. 相似文献
16.
We investigate an exact solution that describes the embedding of the four-dimensional (4D) perfect fluid in a five-dimensional (5D) Einstein spacetime. The effective metric of the 4D perfect fluid as a hypersurface with induced matter is equivalent to the Robertson–Walker metric of cosmology. This general solution shows interconnections among many 5D solutions, such as the solution in the braneworld scenario and the topological black hole with cosmological constant. If the 5D cosmological constant is positive, the metric periodically depends on the extra dimension. Thus we can compactify the extra dimension on S1 and study the phenomenological issues. We also generalize the metric ansatz to the higher-dimensional case, in which the 4D part of the Einstein equations can be reduced to a linear equation. 相似文献
17.
G. Lessner 《General Relativity and Gravitation》2008,40(10):2177-2184
The generation method developed by Newman et al. which creates from spherically symmetric solutions of the field equations
by a complex coordinate transformation axisymmetric solutions is extended to five-dimensional relativity. 相似文献
18.
J. D. Gegenberg 《General Relativity and Gravitation》1989,21(2):155-169
The route from string theory to a ten-dimensional supergravity/super-Yang-Mills field theory is briefly illumined. The process of extracting a classical four-dimensional gravity theory from the ten-dimensional theory is discussed and a simple model containing gravity, electromagnetism, a dilaton field, and a Kalb-Ramond field is proposed. The equations of motion of a test particle in a background of gravity, dilation, and Kalb-Ramond fields are displayed. Some static spherically symmetric vacuum solutions are derived, and some astrophysical implications are discussed. 相似文献
19.
Recently Rizzo studied the Lorentz Invariance Violation (LIV) in a brane scenario with one extra dimension where he found a non-zero mass for the four-dimensional graviton. This leads to the conclusion that five-dimensional models with LIV are not phenomenologically viable. In this work we re-examine the issue of Lorentz Invariance Violation in the context of higher-dimensional theories. We show that a six-dimensional geometry describing a string-like defect with a bulk-dependent cosmological constant can yield a massless 4D graviton, if we allow the cosmological constant variation along the bulk, and thus can provides a phenomenologically viable solution for the gauge hierarchy problem. 相似文献
20.
Yaobing Deng 《General Relativity and Gravitation》1989,21(5):503-507
We study a shear-free spherically symmetric cosmological model with heat flow and present a general method to generate solutions. Using this solution generating scheme we obtain new classes of solutions to the Einstein equations. 相似文献