3,018 research outputs found
Gauss-Bonnet type identity in Weyl-Cartan space
The Gauss-Bonnet type identity is derived in a Weyl-Cartan space on the basis
of the variational method.Comment: 5 page
Is It Really Naked? On Cosmic Censorship in String Theory
We investigate the possibility of cosmic censorship violation in string
theory using a characteristic double-null code, which penetrates horizons and
is capable of resolving the spacetime all the way to the singularity. We
perform high-resolution numerical simulations of the evolution of negative mass
initial scalar field profiles, which were argued to provide a counterexample to
cosmic censorship conjecture for AdS-asymptotic spacetimes in five-dimensional
supergravity. In no instances formation of naked singularity is seen. Instead,
numerical evidence indicates that black holes form in the collapse. Our results
are consistent with earlier numerical studies, and explicitly show where the
`no black hole' argument breaks.Comment: 8 pages, 5 figures, 1 table; REVTeX 4.
The geometry of a naked singularity created by standing waves near a Schwarzschild horizon, and its application to the binary black hole problem
The most promising way to compute the gravitational waves emitted by binary
black holes (BBHs) in their last dozen orbits, where post-Newtonian techniques
fail, is a quasistationary approximation introduced by Detweiler and being
pursued by Price and others. In this approximation the outgoing gravitational
waves at infinity and downgoing gravitational waves at the holes' horizons are
replaced by standing waves so as to guarantee that the spacetime has a helical
Killing vector field. Because the horizon generators will not, in general, be
tidally locked to the holes' orbital motion, the standing waves will destroy
the horizons, converting the black holes into naked singularities that resemble
black holes down to near the horizon radius. This paper uses a spherically
symmetric, scalar-field model problem to explore in detail the following BBH
issues: (i) The destruction of a horizon by the standing waves. (ii) The
accuracy with which the resulting naked singularity resembles a black hole.
(iii) The conversion of the standing-wave spacetime (with a destroyed horizon)
into a spacetime with downgoing waves by the addition of a ``radiation-reaction
field''. (iv) The accuracy with which the resulting downgoing waves agree with
the downgoing waves of a true black-hole spacetime (with horizon). The model
problem used to study these issues consists of a Schwarzschild black hole
endowed with spherical standing waves of a scalar field. It is found that the
spacetime metric of the singular, standing-wave spacetime, and its
radiation-reaction-field-constructed downgoing waves are quite close to those
for a Schwarzschild black hole with downgoing waves -- sufficiently close to
make the BBH quasistationary approximation look promising for
non-tidally-locked black holes.Comment: 12 pages, 6 figure
Quasinormal Modes of Charged Scalars around Dilaton Black Holes in 2+1 Dimensions: Exact Frequencies
We have studied the charged scalar perturbation around a dilaton black hole
in 2 +1 dimensions. The wave equations of a massless charged scalar field is
shown to be exactly solvable in terms of hypergeometric functions. The
quasinormal frequencies are computed exactly. The relation between the
quasinormal frequencies and the charge of the black hole, charge of the scalar
and the temperature of the black hole are analyzed. The asymptotic form of the
real part of the quasinormal frequencies are evaluated exactly.Comment: 20 pages and 7 figures, some references are added and some removed.
There are some changes to the text. arXiv admin note: text overlap with
arXiv:hep-th/040716
Plane torsion waves in quadratic gravitational theories
The definition of the Riemann-Cartan space of the plane wave type is given.
The condition under which the torsion plane waves exist is found. It is
expressed in the form of the restriction imposed on the coupling constants of
the 10-parametric quadratic gravitational Lagrangian. In the mathematical
appendix the formula for commutator of the variation operator and Hodge
operator is proved. This formula is applied for the variational procedure when
the gravitational field equations are obtained in terms of the exterior
differential forms.Comment: 3 May 1998. - 11
Development of Current Limiting Device for Short and Autonomous Networks
In this paper, the problem of tripping of high values of short-circuit currents in mediumvoltage networks will be considered. Disconnection of short-circuit currents which can reach 100–300 kA in short networks is difficult task for modern switching equipment due to the impossibility of damping the electric arc generated by such currents, and due to strong thermal and electrodynamic effects on elements of the switching device. Solution based on active current limiting reactor will be presented
Proper Motions and CCD-photometry of Stars in the Region of the Open Cluster Trumpler 2
The results of the complex study of galactic open cluster Trumpler 2 are
presented. In order to obtain the proper motions the positions of 2600 stars up
to the limit magnitude B ~ 16.25 mag in the area 80x80 arcmin around the
cluster were measured on 6 plates with the maximal epoch difference of 63
years. The root-mean error of the relative proper motions is 4.2 mas/yr. The
catalogue of BV magnitudes of all the stars in the investigated area was
compiled. Astrometric selection of the cluster members within the region of
R<16 arcmin from the center of the cluster was made by means of the W.Sanders
method. In that field 192 stars were found to have the individual membership
probability greater then 85%, 148 of them are situated within the
+/-3sigma_(B-V) band around the main sequence of the cluster. They are
considered to be cluster members by two criteria. The U-B ~ B-V diagram plotted
for the astrometrical cluster members by the data taken from the Washington
catalogue of the UBV photometry in the galactic cluster fields (Hoag et
al.1961) made it possible to redefine the value of the color excess E(B-V)=0.40
mag. The superposition of the MS of the cluster with the ZAMS Schmidt-Kaler
leads to the coincidence at the value of the apparent distance module
(V-Mv)=10.50 which corresponds to the distance r=725 pc. The luminosity and
mass functions of the Trumpler 2 were constructed and the value of the slope
Gamma=-1.90+/-0.22 was determined. The cluster age of 8.913x10^7 yr was
determined. It is shown that the red giant on the late stage of the evolution
(st N.1095) belongs to cluster and indicates the brightness variability. The
possibility that the number of both known and recently discovered variables are
cluster members was considered. Tables 2,3,3A,5 will be only available in the
electronic form.Comment: 14 pages, 7 figure
Action and Hamiltonian for eternal black holes
We present the Hamiltonian, quasilocal energy, and angular momentum for a
spacetime region spatially bounded by two timelike surfaces. The results are
applied to the particular case of a spacetime representing an eternal black
hole. It is shown that in the case when the boundaries are located in two
different wedges of the Kruskal diagram, the Hamiltonian is of the form , where and are the Hamiltonian functions for the right
and left wedges respectively. The application of the obtained results to the
thermofield dynamics description of quantum effects in black holes is briefly
discussed.Comment: 24 pages, Revtex, 5 figures (available upon request
Analytic Evaluation of Four-Particle Integrals with Complex Parameters
The method for analytic evaluation of four-particle integrals, proposed by
Fromm and Hill, is generalized to include complex exponential parameters. An
original procedure of numerical branch tracking for multiple valued functions
is developed. It allows high precision variational solution of the Coulomb
four-body problem in a basis of exponential-trigonometric functions of
interparticle separations. Numerical results demonstrate high efficiency and
versatility of the new method.Comment: 13 pages, 4 figure
Dynamical excitation of space-time modes of compact objects
We discuss, in the perturbative regime, the scattering of Gaussian pulses of
odd-parity gravitational radiation off a non-rotating relativistic star and a
Schwarzschild Black Hole. We focus on the excitation of the -modes of the
star as a function of the width of the pulse and we contrast it with the
outcome of a Schwarzschild Black Hole of the same mass. For sufficiently narrow
values of , the waveforms are dominated by characteristic space-time modes.
On the other hand, for sufficiently large values of the backscattered
signal is dominated by the tail of the Regge-Wheeler potential, the
quasi-normal modes are not excited and the nature of the central object cannot
be established. We view this work as a useful contribution to the comparison
between perturbative results and forthcoming -mode 3D-nonlinear numerical
simulation.Comment: RevTeX, 9 pages, 7 figures, Published in Phys. Rev.
- …