arXiv
(422.153 recursos)
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Mostrando recursos 1 - 20 de 26.395
1.
Spherically symmetric spacetimes with a trapped surface - Dafermos, Mihalis
This paper investigates the global properties of a class of spherically
symmetric spacetimes. The class contains the maximal development of
asymptotically flat spherically symmetric initial data for a wide variety of
coupled Einstein-matter systems. For this class, it is proven here that the
existence of a single trapped surface or marginally trapped surface implies the
completeness of future null infinity and the formation of an event horizon
whose area radius is bounded by twice the final Bondi mass.
2.
Sagnac Effect of Goedel's Universe - Kajari, E.; Walser, R.; Schleich, W. P.; Delgado, A.
We present exact expressions for the Sagnac effect of Goedel's Universe. For
this purpose we first derive a formula for the Sagnac time delay along a
circular path in the presence of an arbitrary stationary metric in cylindrical
coordinates. We then apply this result to Goedel's metric for two different
experimental situations: First, the light source and the detector are at rest
relative to the matter generating the gravitational field. In this case we find
an expression that is formally equivalent to the familiar nonrelativistic
Sagnac time delay. Second, the light source and the detector are rotating
relative to the matter. Here we show that for a special...
3.
Area Regge Calculus and Discontinuous Metrics - Wainwright, Chris; Williams, Ruth M.
Taking the triangle areas as independent variables in the theory of Regge
calculus can lead to ambiguities in the edge lengths, which can be interpreted
as discontinuities in the metric. We construct solutions to area Regge calculus
using a triangulated lattice and find that on a spacelike hypersurface no such
discontinuity can arise. On a null hypersurface however, we can have such a
situation and the resulting metric can be interpreted as a so-called refractive
wave.
4.
Critical Collapse of a Complex Scalar Field with Angular Momentum - Choptuik, M. W.; Hirschmann, E. W.; Liebling, S. L.; Pretorius, F.
We report a new critical solution found at the threshold of axisymmetric
gravitational collapse of a complex scalar field with angular momentum. To
carry angular momentum the scalar field cannot be axisymmetric; however, its
azimuthal dependence is defined so that the resulting stress energy tensor and
spacetime metric are axisymmetric. The critical solution found is
non-spherical, discretely self-similar with an echoing exponent of 0.42 (+-
4%), and exhibits a scaling exponent of 0.11 (+- 10%) in near critical
collapse. Our simulations suggest that the solution is universal (within the
imposed symmetry class), modulo a family-dependent constant phase in the
complex plane.
5.
Entropy in the NUT-Kerr-Newman Black Holes Due to an Arbitrary Spin Field - Ge, Xian-Hui; Shen, You-Gen
Membrane method is used to compute the entropy of the NUT-Kerr-Newman black
holes. It is found that even though the Euler characteristic is greater than
two, the Bekenstein-Hawking area law is still satisfied. The formula $S=\chi
A/8$ relating the entropy and the Euler characteristic becomes inapplicable for
non-extreme four dimensional NUT-Kerr-Newman black holes.
6.
Geodesics in a Toroidal space-time - Wickramasuriya, S. B. P.; Joseph, V.; Karunaratne, K. I. S.
We take a three dimensional Euclidian metric in toroidal coordinates and
consider the corresponding Laplace equation. The simplest solution of this
equation is taken. Based on this we build a Weyl space-time. This space-time is
transformed to cylindrical coordinates. It is shown by using Mathematica that
Weyl equations in cylindrical coordinates are satisfied. Geodesic motion is
considered along the symmetric axis as well as along the radii of the
singularity, which is the cause of the space time.
7.
Role of Modified Chaplygin Gas in Accelerated Universe - Debnath, Ujjal; Banerjee, Asit; Chakraborty, Subenoy
In this paper we have considered a model of modified Chaplygin gas and its
role in accelerating phase of the universe. We have assumed that the equation
of state of this modified model is valid from the radiation era to $\Lambda$CDM
model. We have used recently developed statefinder parameters in characterizing
different phase of the universe diagrammatically.
8.
Krein space quantization in curved and flat spacetimes - Garidi, T.; Huguet, E.; Renaud, J.
We reexamine in detail a canonical quantization method a la Gupta-Bleuler in
which the Fock space is built over a so-called Krein space. This method has
already been successfully applied to the massless minimally coupled scalar
field in de Sitter spacetime for which it preserves covariance. Here, it is
formulated in a more general context. An interesting feature of the theory is
that, although the field is obtained by canonical quantization, it is
independent of Bogoliubov transformations. Moreover no infinite term appears in
the computation of $T^{\mu\nu}$ mean values and the vacuum energy of the free
field vanishes: $<0|T^{00}|0>=0$. We also investigate the behaviour of the
Krein quantization in...
9.
Evolution equations for slowly rotating stars - Stavridis, Adamantios; Kokkotas, Kostas D.
We present a hyperbolic formulation of the evolution equations describing
non-radial perturbations of slowly rotating relativistic stars in the
Regge--Wheeler gauge. We demonstrate the stability preperties of the new
evolution set of equations and compute the polar w-modes for slowly rotating
stars.
10.
Mathematical Structure of Tetrad Equations for Vacuum Relativity - Estabrook, Frank B.
The tetrad partial differential equations formulated by Buchman and Bardeen
for vacuum gravity are shown to be well posed by calculation of the Cartan
characters of an associated exterior differential system. Gauge specializations
are discussed. A Cartan 4-form is found for this field theory, together with
its intrinsic version the Lagrangian density.
11.
Alignment and the classification of Lorentz-signature tensors - Milson, Robert
We define the notion of an aligned null direction, a Lorentz-signature
analogue of the eigenvector concept that is valid for arbitrary tensor types.
The set of aligned null directions is described by a a system of alignment
polynomials whose coefficients are derived from the components of the tensor.
The algebraic properties of the alignment polynomials can be used to classify
the corresponding tensors and to put them into normal form. The alignment
classification paradigm is illustrated with a discussion of bivectors and of
Weyl-type tensors. Note: an earlier version of this manuscript was published in
the proceedings of SPT 2004. The present version has been expanded to include...
12.
Twisted Electromagnetic Modes and Sagnac Ring-Lasers - Burton, David A.; Noble, Adam; Tucker, Robin W.; Wiltshire, David L.
A new approximation scheme, designed to solve the covariant Maxwell equations
inside a rotating hollow slender conducting cavity (modelling a ring-laser), is
constructed. It is shown that for well-defined conditions there exist TE and TM
modes with respect to the longitudinal axis of the cavity. A twisted mode
spectrum is found to depend on the integrated Frenet torsion of the cavity and
this in turn may affect the Sagnac beat frequency induced by a non-zero
rotation of the cavity. The analysis is motivated by attempts to use
ring-lasers to measure terrestrial gravito-magnetism or the Lense-Thirring
effect produced by the rotation of the Earth.
13.
On the Physical Hilbert Space of Loop Quantum Cosmology - Noui, Karim; Perez, Alejandro; Vandersloot, Kevin
In this paper we present a model of Riemannian loop quantum cosmology with a
self-adjoint quantum scalar constraint. The physical Hilbert space is
constructed using refined algebraic quantization. When matter is included in
the form of a cosmological constant, the model is exactly solvable and we show
explicitly that the physical Hilbert space is separable consisting of a single
physical state. We extend the model to the Lorentzian sector and discuss
important implications for standard loop quantum cosmology.
14.
Quasinormal Ringing for Acoustic Black Holes at Low Temperature - Nakano, Hiroyuki; Kurita, Yasunari; Ogawa, Kouji; Yoo, Chul-Moon
We investigate a condensed matter ``black hole'' analogue, taking the
Gross-Pitaevskii (GP) equation as a starting point. The linearized GP equation
corresponds to a wave equation on a black hole background, giving quasinormal
modes under some appropriate conditions. We suggest that we can know the
detailed characters and corresponding geometrical information about the
acoustic black hole by observing quasinormal ringdown waves in the low
temperature condensed matters.
15.
Vacuum polarization around stars: nonlocal approximation - Satz, Alejandro; Mazzitelli, Francisco D.; Alvarez, Ezequiel
We compute the vacuum polarization associated with quantum massless fields
around stars with spherical symmetry. The nonlocal contribution to the vacuum
polarization is dominant in the weak field limit, and induces quantum
corrections to the exterior metric that depend on the inner structure of the
star. It also violates the null energy conditions. We argue that similar
results also hold in the low energy limit of quantum gravity. Previous
calculations of the vacuum polarization in spherically symmetric spacetimes,
based on local approximations, are not adequate for newtonian stars.
16.
Quantization of the Classical Maxwell-Nordstrom Fields - Kocinski, J.
The classical electromagnetic and gravitomagnetic fields in the vacuum, in
(3+2) dimensions, described by the Maxwell-Nordstrom equations, are quantized.
These equations are rederived from the field tensor which follows from a
five-dimensional form of the Dirac equation. The electromagnetic field depends
on the customary time t, and the hypothetical gravitomagnetic field depends on
the second time variable u. The total field energy is identified with the
component T44 of the five-dimensional energy-stress tensor of the
electromagnetic and gravitomagnetic fields. In the ground state, the
electromagnetic field and the gravitomagnetic field energies cancel out. The
quanta of the gravitomagnetic field have spin 1.
17.
A Coherent Strategy for Qauntum Gravity - Klauder, John R.
Affine quantum gravity, which differs notably from either string theory or
loop quantum gravity, is briefly reviewed. Emphasis in this article is placed
on the use of affine coherent states in this program.
18.
Attractions of Affine Quantum Gravity - Klauder, John R.
All attempts to quantize gravity face several difficult problems. Among these
problems are: (i) metric positivity (positivity of the spatial distance between
distinct points), (ii) the presence of anomalies (partial second-class nature
of the quantum constraints), and (iii) perturbative nonrenormalizability (the
need for infinitely many distinct counterterms). In this report, a relatively
nontechnical discussion is presented about how the program of affine quantum
gravity proposes to deal with these problems.
19.
Decay of massive scalar field in a Schwarzschild background - Konoplya, R. A.; Zhidenko, A. V.
The decay of massive scalar field in the Schwarzschild black hole background
is investigated here by consideration its quasinormal spectrum. It has been
proved that the so-called $quasi-resonant$ modes, which are arbitrary long
living (purely real) modes, can exist only if the effective potential is not
zero at least at one of the boundaries of the $R$-region. We have observed that
the quasinormal spectrum exists for all field masses and proved both
analytically and numerically that when $n \to \infty$ the real part of the
frequencies approaches the same asymptotical value ($\ln3/(8\pi M)$) as in the
case of the massless field.
20.
Conformal continuations and wormhole instability in scalar-tensor gravity - Bronnikov, K. A.; Grinyok, S. V.
We study the stability of static, spherically symmetric, traversable
wormholes existing due to conformal continuations in a class of scalar-tensor
theories with zero scalar field potential (so that Fisher's well-known
scalar-vacuum solution holds in the Einstein conformal frame). Specific
examples of such wormholes are those with nonminimally (e.g., conformally)
coupled scalar fields. All boundary conditions for scalar and metric
perturbations are taken into account. All such wormholes are shown to be
unstable under spherically symmetric perturbations. The instability is proved
analytically with the aid of the theory of self-adjoint operators in Hilbert
space and is confirmed by a numerical computation.
1.
