463 research outputs found
Pulsation of Spherically Symmetric Systems in General Relativity
The pulsation equations for spherically symmetric black hole and soliton
solutions are brought into a standard form. The formulae apply to a large class
of field theoretical matter models and can easily be worked out for specific
examples. The close relation to the energy principle in terms of the second
variation of the Schwarzschild mass is also established. The use of the general
expressions is illustrated for the Einstein-Yang-Mills and the Einstein-Skyrme
system.Comment: 21 pages, latex, no figure
Substituting the main group element in cobalt - iron based Heusler alloys: CoFeAlSi
This work reports about electronic structure calculations for the Heusler
compound CoFeAlSi. Particular emphasis was put on the role of
the main group element in this compound. The substitution of Al by Si leads to
an increase of the number of valence electrons with increasing Si content and
may be seen as electron-doping. Self-consistent electronic structure
calculations were performed to investigate the consequences of the electron
doping for the magnetic properties. The series CoFeAlSi is
found to exhibit half-metallic ferromagnetism and the magnetic moment follows
the Slater-Pauling rule. It is shown that the electron-doping stabilises the
gap in the minority states for .Comment: J. Phys. D (accepted
Higher-dimensional solitons and black holes with a non-minimally coupled scalar field
We study higher-dimensional soliton and hairy black hole solutions of the
Einstein equations non-minimally coupled to a scalar field. The scalar field
has no self-interaction potential but a cosmological constant is included.
Non-trivial solutions exist only when the cosmological constant is negative and
the constant governing the coupling of the scalar field to the Ricci scalar
curvature is positive. At least some of these solutions are stable when this
coupling constant is not too large.Comment: 17 pages, revtex4, 21 figures, minor changes to match published
versio
Evolution of a Self-interacting Scalar Field in the spacetime of a Higher Dimensional Black Hole
In the spacetime of n-dimensional static charged black hole we examine the
mechanism by which the self-interacting scalar hair decay. It is turned out
that the intermediate asymptotic behaviour of the self-interacting scalar field
is determined by an oscilatory inverse power law. We confirm our results by
numerical calculations.Comment: RevTex, 6 pages, 8 figures, to be published in Phys.Rev.D1
On Black Hole Scalar Hair in Asymptotically Anti de Sitter Spacetimes
The unexpected discovery of hairy black hole solutions in theories with
scalar fields simply by considering asymptotically Anti de-Sitter, rather than
asymptotically flat, boundary conditions is analyzed in a way that exhibits in
a clear manner the differences between the two situations.
It is shown that the trivial Schwarzschild Anti de Sitter becomes unstable in
some of these situations, and the possible relevance of this fact for the
ADS/CFT conjecture is pointed out.Comment: 12 pages. Published versio
Mode coupling of Schwarzschild perturbations: Ringdown frequencies
Within linearized perturbation theory, black holes decay to their final
stationary state through the well-known spectrum of quasinormal modes. Here we
numerically study whether nonlinearities change this picture. For that purpose
we study the ringdown frequencies of gauge-invariant second-order gravitational
perturbations induced by self-coupling of linearized perturbations of
Schwarzschild black holes. We do so through high-accuracy simulations in the
time domain of first and second-order Regge-Wheeler-Zerilli type equations, for
a variety of initial data sets. We consider first-order even-parity
perturbations and odd-parity ones, and all
the multipoles that they generate through self-coupling. For all of them and
all the initial data sets considered we find that ---in contrast to previous
predictions in the literature--- the numerical decay frequencies of
second-order perturbations are the same ones of linearized theory, and we
explain the observed behavior. This would indicate, in particular, that when
modeling or searching for ringdown gravitational waves, appropriately including
the standard quasinormal modes already takes into account nonlinear effects
Dynamical Collapse of Charged Scalar Field in Phantom Gravity
We investigated the problem of the dynamical collapse of a self-gravitating
complex charged scalar field in Einstein-Maxwell-dilaton theory with a phantom
copuling for the adequate fields in the system under consideration. We also
considered two simplifications of it, i.e., the separate collapses of phantom
Maxwell and phantom scalar fields under the influence of Einstein gravity. One
starts with the regular spacetime and leads the evolution through the formation
of the horizons and the final singularity. We discuss the structures of
spacetimes emerging in the process of the dynamical collapse and comment on the
role of the considered fields in its course.Comment: 15 pages, RevTex, 18 figures, to be published in Phys.Rev.D1
Semiclassical Approach to Chaotic Quantum Transport
We describe a semiclassical method to calculate universal transport
properties of chaotic cavities. While the energy-averaged conductance turns out
governed by pairs of entrance-to-exit trajectories, the conductance variance,
shot noise and other related quantities require trajectory quadruplets; simple
diagrammatic rules allow to find the contributions of these pairs and
quadruplets. Both pure symmetry classes and the crossover due to an external
magnetic field are considered.Comment: 33 pages, 11 figures (appendices B-D not included in journal version
Semiclassical Theory for Parametric Correlation of Energy Levels
Parametric energy-level correlation describes the response of the
energy-level statistics to an external parameter such as the magnetic field.
Using semiclassical periodic-orbit theory for a chaotic system, we evaluate the
parametric energy-level correlation depending on the magnetic field difference.
The small-time expansion of the spectral form factor is shown to be
in agreement with the prediction of parameter dependent random-matrix theory to
all orders in .Comment: 25 pages, no figur
THE UNIQUENESS THEOREM FOR ROTATING BLACK HOLE SOLUTIONS OF SELF-GRAVITATING HARMONIC MAPPINGS
We consider rotating black hole configurations of self-gravitating maps from
spacetime into arbitrary Riemannian manifolds. We first establish the
integrability conditions for the Killing fields generating the stationary and
the axisymmetric isometry (circularity theorem). Restricting ourselves to
mappings with harmonic action, we subsequently prove that the only stationary
and axisymmetric, asymptotically flat black hole solution with regular event
horizon is the Kerr metric. Together with the uniqueness result for
non-rotating configurations and the strong rigidity theorem, this establishes
the uniqueness of the Kerr family amongst all stationary black hole solutions
of self-gravitating harmonic mappings.Comment: 18 pages, latex, no figure
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