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1.
In addition to the Kerr-Newman metric with cosmological constant several other metrics are presented giving Kerr-Newman type
solutions of Einstein-Maxwell field equations in the background of deSitter universe. The electromagnetic field in all the
solutions is assumed to be source-free. A new metric of what may be termed as an electrovac rotating de-Sitter space-time—a
space-time devoid of matter but containing source-free electromagnetic field and a null fluid with twisting rays—has been
presented. In the absence of the electromagnetic field, our solutions reduce to those discussed by Vaidya. 相似文献
2.
P C Vaidya 《Pramana》1977,8(6):512-517
A metric satisfying Einstein’s equations is given which in the vicinity of the source reduces to the well-known Kerr metric
and which at large distances reduces to the Robertson-Walker metric of a homogeneous cosmological model. The radius of the
event horizon of the Kerr black hole in the cosmological background is found out. 相似文献
3.
Spherically symmetric non-static higher dimensional metrics are considered in connection with Einstein’s field equations.
Two exact solutions are derived. One of them corresponds to a mixture of perfect fluid and pure radiation field and represents
higher dimensional Vaidya metric in the cosmological background of Einstein static universe. The other corresponds to a pure
radiation field and represents higher dimensional Vaidya metric in the background de Sitter universe. For both of these solutions,
the cosmological constant is taken to be non-zero. Many known solutions are derived as particular cases. 相似文献
4.
It is shown that every type {22} vacuum solution of Einstein's equations admits a quadratic first integral of the null geodesic equations (conformal Killing tensor of valence 2), which is independent of the metric and of any Killing vectors arising from symmetries. In particular, the charged Kerr solution (with or without cosmological constant) is shown to admit a Killing tensor of valence 2. The Killing tensor, together with the metric and the two Killing vectors, provides a method of explicitly integrating the geodesics of the (charged) Kerr solution, thus shedding some light on a result due to Carter. 相似文献
5.
Subodha Mishra 《International Journal of Theoretical Physics》2008,47(10):2655-2662
Considering our expanding universe as made up of gravitationally interacting particles which describe particles of luminous
matter, dark matter and dark energy which is represented by a repulsive harmonic potential among the points in the flat 3-space
and incorporating Mach’s principle into our theory, we derive a quantum mechanical relation connecting, temperature of the
cosmic microwave background radiation, age, and cosmological constant of the universe. When the cosmological constant is zero,
we get back Gamow’s relation with a much better coefficient. Otherwise, our theory predicts a value of the cosmological constant
2.0×10−56 cm−2 when the present values of cosmic microwave background temperature of 2.728 K and age of the universe 14 billion years are
taken as input. 相似文献
6.
P C Vaidya 《Pramana》1985,25(5):513-518
A metric containing a parameterb is presented. It represents two distinct families of space-times, the Taub-nut family and the deSitter family, according asb=1 andb=4 respectively.
The metric of the deSitter family of space-times contains a further parameterm. Whenm=0, the space-time is the usual homogeneous and isotropic deSitter space-time. But ifm≠0, the metric represents a space-time which is homogeneous but not isotropic satisfyingR
ik
=Λg
ik
. In this space-time, the 4-velocity of an observer at rest will have non-zero twist. The metric withb=4,m≠0 is interpreted as a metric representing a “rotating deSitter space-time”. 相似文献
7.
Spatially homogeneous and anisotropic LRS Bianchi type-I metric is considered in the framework of Nordtvedt-Barker’s general
scalar-tensor theory of gravitation when the source for the energy momentum tensor is a perfect fluid. With the help of a
special law of variation for Hubble’s parameter proposed by Berman (Nuovo Cim. B. 74:182, 1983) a cosmological model with negative constant deceleration parameter is obtained. Some physical and kinematical properties
of the model are also discussed. 相似文献
8.
T. Padmanabhan 《General Relativity and Gravitation》2008,40(2-3):529-564
I review the problem of dark energy focussing on cosmological constant as the candidate and discuss what it tells us regarding
the nature of gravity. Section 1 briefly overviews the currently popular “concordance cosmology” and summarizes the evidence
for dark energy. It also provides the observational and theoretical arguments in favour of the cosmological constant as a
candidate and emphasizes why no other approach really solves the conceptual problems usually attributed to cosmological constant.
Section 2 describes some of the approaches to understand the nature of the cosmological constant and attempts to extract certain
key ingredients which must be present in any viable solution. In the conventional approach, the equations of motion for matter
fields are invariant under the shift of the matter Lagrangian by a constant while gravity breaks this symmetry. I argue that
until the gravity is made to respect this symmetry, one cannot obtain a satisfactory solution to the cosmological constant
problem. Hence cosmological constant problem essentially has to do with our understanding of the nature of gravity. Section 3 discusses such an alternative perspective on gravity in which the gravitational interaction—described in terms
of a metric on a smooth spacetime—is an emergent, long wavelength phenomenon, and can be described in terms of an effective
theory using an action associated with normalized vectors in the spacetime. This action is explicitly invariant under the
shift of the matter energy momentum tensor T
ab
→ T
ab
+ Λ
gab
and any bulk cosmological constant can be gauged away. Extremizing this action leads to an equation determining the background geometry which gives Einstein’s theory at the lowest order with Lanczos–Lovelock type corrections. In this approach, the observed
value of the cosmological constant has to arise from the energy fluctuations of degrees of freedom located in the boundary
of a spacetime region. 相似文献
9.
A spatially homogeneous and anisotropic Bianchi type-I perfect fluid model is considered with variable cosmological constant.
Einstein’s field equations are solved by using a law of variation for mean Hubble’s parameter, which is related to average
scale factor and that yields a constant value of deceleration parameter. An exact and singular Bianchi-I model is presented,
where the cosmological constant remains positive and decreases with the cosmic time. It is found that the solutions are consistent
with the recent observations of type Ia supernovae. A detailed study of physical and kinematical properties of the model is
carried out. 相似文献
10.
J. P. Singh 《International Journal of Theoretical Physics》2009,48(7):2041-2049
In the present paper, we investigate the possibility of a variation law for Hubble’s parameter H in the background of spatially homogeneous, anisotropic Bianchi type V space-time with perfect fluid source and time-dependent
cosmological term. The model obtained presents a cosmological scenario which describes an early deceleration and late time
acceleration. The model approaches isotropy and tends to a de Sitter universe at late times. The cosmological term Λ asymptotically
tends to a genuine cosmological constant. It is observed that the solution is consistent with the results of recent observations. 相似文献
11.
Gregory J. Galloway Kristin Schleich Donald M. Witt 《Communications in Mathematical Physics》2012,310(2):285-298
We use existence results for Jang’s equation and marginally outer trapped surfaces (MOTSs) in 2 + 1 gravity to obtain nonexistence
of geons in 2 + 1 gravity. In particular, our results show that any 2 + 1 initial data set, which obeys the dominant energy
condition with cosmological constant Λ ≥ 0 and which satisfies a mild asymptotic condition, must have trivial topology. Moreover,
any data set obeying these conditions cannot contain a MOTS. The asymptotic condition involves a cutoff at a finite boundary
at which a null mean convexity condition is assumed to hold; this null mean convexity condition is satisfied by all the standard
asymptotic boundary conditions. The results presented here strengthen various aspects of previous related results in the literature.
These results not only have implications for classical 2 + 1 gravity but also apply to quantum 2 + 1 gravity when formulated
using Witten’s solution space quantization. 相似文献
12.
A method of obtaining solutions of Einstein field equations, representing rotating type II null fluids is presented. One explicit
solution is given and its details are discussed. The well-known deSitter metric is derived as a particular case. 相似文献
13.
We present the general junction conditions for the smooth matching of a spherically symmetric, shear-free spacetime to Vaidya’s
outgoing metric across a four-dimensional time-like hypersurface in the presence of a cosmological constant. These results
generalise earlier treatments by Santos and co-workers on radiating stellar models. We study the thermal evolution of a particular
radiating model within the framework of extended irreversible thermodynamics. 相似文献
14.
Dynamic and static wormhole solutions of Einsteins equations with the cosmological constant are presented. The dynamic solutions can be interpreted as Friedmann–Robertson–Walker models with traversable wormholes. The null energy condition is checked for both dynamic and static wormholes and it is shown explicitly that the cosmological constant modifies the violation of this condition. 相似文献
15.
K S Virbhadra 《Pramana》1993,40(4):273-275
An exact solution of Einstein’s equations is interpreted as describing the gravitational field of a tachyon in a de Sitter
universe. Switching off the cosmological constant yields the gravitational field of a tachyon in flat spacetime background. 相似文献
16.
Brandon Carter 《General Relativity and Gravitation》2009,41(12):2873-2938
This is a reprinting of Part 1 of Brandon Carter’s lectures given at the 1972 Les Houches school on black holes, first published
in a book of proceedings of that school in 1973. The paper has been selected by the Editors of General Relativity and Gravitation
for re-publication in the Golden Oldies series of the journal. The main value of this article is a comprehensive discussion
of global properties of the Kerr solution, its maximal extension, its derivation from the separability of the Klein-Gordon
equation and, most notably, its generalisation to nonzero cosmological constant. Numerous typos of the original text are corrected
in this reprinting. The reprinted article is accompanied by an editorial note written by Niky Kamran and Andrzej Krasiński,
and by B. Carter’s brief autobiography. 相似文献
17.
R. P. Wallner 《General Relativity and Gravitation》1991,23(6):623-639
We investigate the energy-momentum and spin field equations of gravity theory on a Riemann-Cartan space-time (including metric and torsion,U
4-manifold). The structure of the rather complicated nonlinear differential equations of second order is made considerably easier to survey by decomposing curvature into its self and anti-self double dual parts. This leads to an obvious ansatz for the self double dual curvature, whereby the field equations are reduced to Einstein's equations with cosmological term. To solve the double dual ansatz, we choose proper variables adopted to its double duality, and perform a (3+1)-decomposition of exterior calculus. We examine these equations further on a Kerr background with cosmological constant for the Riemannian geometry. 相似文献
18.
The cosmological constant problem is examined within the context of the covariant brane-world gravity, based on Nash’s embedding
theorem for Riemannian geometries. We show that the vacuum structure of the brane-world is more complex than General Relativity’s
because it involves extrinsic elements, in specific, the extrinsic curvature. In other words, the shape (or local curvature)
of an object becomes a relative concept, instead of the “absolute shape” of General Relativity. We point out that the immediate
consequence is that the cosmological constant and the energy density of the vacuum quantum fluctuations have different physical
meanings: while the vacuum energy density remains confined to the four-dimensional brane-world, the cosmological constant
is a property of the bulk’s gravitational field that leads to the conclusion that these quantities cannot be compared, as
it is usually done in General Relativity. Instead, the vacuum energy density contributes to the extrinsic curvature, which
in turn generates Nash’s perturbation of the gravitational field. On the other hand, the cosmological constant problem ceases
to be in the brane-world geometry, reappearing only in the limit where the extrinsic curvature vanishes. 相似文献
19.
The techniques of second quantization in Kerr metric for the scalar and neutrino (massless) fields are extended to the massive
spin half case. The normal modes of Dirac field in Kerr metric are obtained in Chandrasekhar’s representation and the field
is quantized as usual by imposing equal-time anti-commutation relations. The vacuum expectation value of energy-momentum tensor
is evaluated asymptotically, leading to the result that a Kerr black hole spontaneously creates, in addition to scalar and
neutrino quanta, massive Dirac particles in the classical superradiant modes. 相似文献
20.
Nikodem?J.?Pop?awski 《Foundations of Physics》2009,39(3):307-330
The Ferraris-Kijowski purely affine Lagrangian for the electromagnetic field, that has the form of the Maxwell Lagrangian
with the metric tensor replaced by the symmetrized Ricci tensor, is dynamically equivalent to the metric Einstein-Maxwell
Lagrangian, except the zero-field limit, for which the metric tensor is not well-defined. This feature indicates that, for
the Ferraris-Kijowski model to be physical, there must exist a background field that depends on the Ricci tensor. The simplest
possibility, supported by recent astronomical observations, is the cosmological constant, generated in the purely affine formulation
of gravity by the Eddington Lagrangian. In this paper we combine the electromagnetic field and the cosmological constant in
the purely affine formulation. We show that the sum of the two affine (Eddington and Ferraris-Kijowski) Lagrangians is dynamically
inequivalent to the sum of the analogous (ΛCDM and Einstein-Maxwell) Lagrangians in the metric-affine/metric formulation. We also show that such a construction is valid,
like the affine Einstein-Born-Infeld formulation, only for weak electromagnetic fields, on the order of the magnetic field
in outer space of the Solar System. Therefore the purely affine formulation that combines gravity, electromagnetism and cosmological
constant cannot be a simple sum of affine terms corresponding separately to these fields. A quite complicated form of the
affine equivalent of the metric Einstein-Maxwell-Λ Lagrangian suggests that Nature can be described by a simpler affine Lagrangian, leading to modifications of the Einstein-Maxwell-ΛCDM theory for electromagnetic fields that contribute to the spacetime curvature on the same order as the cosmological constant. 相似文献