3,153 research outputs found
Physical Processes in Naked Singularity Formation
Gravitational collapse is one of the most fruitful subjects in gravitational
physics. It is well known that singularity formation is inevitable in complete
gravitational collapse. It was conjectured that such a singularity should be
hidden by horizons if it is formed from generic initial data with physically
reasonable matter fields. Many possible counterexamples to this conjecture have
been proposed over the past three decades, although none of them has proved to
be sufficiently generic. In these examples, there appears a singularity that is
not hidden by horizons. This singularity is called a `naked singularity.' The
appearance of a naked singularity represents the formation of an observable
high-curvature, strong-gravity region. In this paper we review examples of
naked singularity formation and recent progress in research of observable
physical processes - gravitational radiation and quantum particle creation -
from a forming naked singularity.Comment: 76 pages, 25 figure file
The Bell-Szekeres Solution and Related Solutions of the Einstein-Maxwell Equations
A novel technique for solving some head-on collisions of plane homogeneous
light-like signals in Einstein-Maxwell theory is described. The technique is a
by-product of a re-examination of the fundamental Bell-Szekeres solution in
this field of study. Extensions of the Bell-Szekeres collision problem to
include light-like shells and gravitational waves are described and a family of
solutions having geometrical and topological properties in common with the
Bell-Szekeres solution is derived.Comment: 18 pages, Latex fil
Perturbations and Stability of Black Ellipsoids
We study the perturbations of two classes of static black ellipsoid solutions
of four dimensional vacuum Einstein equations. Such solutions are described by
generic off--diagonal metrics which are generated by anholonomic transforms of
diagonal metrics. The analysis is performed in the approximation of small
eccentricity deformations of the Schwarzschild solution. We conclude that such
anisotropic black hole objects may be stable with respect to the perturbations
parametrized by the Schrodinger equations in the framework of the
one--dimensional inverse scattering theory.Comment: Published variant in IJMD with small modifications in formulas and
new reference
Gravitational Radiation from a Naked Singularity -- Odd-Parity Perturbation --
It has been suggested that a naked singularity may be a good candidate for a
strong gravitational wave burster. The naked singularity occurs in the generic
collapse of an inhomogeneous dust ball. We study odd-parity mode of
gravitational waves from a naked singularity of the Lema\^{\i}tre-Tolman-Bondi
space-time. The wave equation for gravitational waves are solved by numerical
integration using the single null coordinate. The result is that the naked
singularity is not a strong source of the odd-parity gravitational radiation
although the metric perturbation grows in the central region. Therefore, the
Cauchy horizon in this space-time would be marginally stable against odd-parity
perturbations.Comment: 14 pages, 7 figures, to be published in Prog. Theor. Phys. Final
version, with minor changes. Reference 13 adde
Binaries and core-ring structures in self-gravitating systems
Low energy states of self-gravitating systems with finite angular momentum
are considered. A constraint is introduced to confine cores and other condensed
objects within the system boundaries by gravity alone. This excludes previously
observed astrophysically irrelevant asymmetric configurations with a single
core. We show that for an intermediate range of a short-distance cutoff and
small angular momentum, the equilibrium configuration is an asymmetric binary.
For larger angular momentum or for a smaller range of the short distance
cutoff, the equilibrium configuration consists of a central core and an
equatorial ring. The mass of the ring varies between zero for vanishing
rotation and the full system mass for the maximum angular momentum a
localized gravitationally bound system can have. The value of scales
as , where is a ratio of a short-distance cutoff range
to the system size. An example of the soft gravitational potential is
considered; the conclusions are shown to be valid for other forms of
short-distance regularization.Comment: 6 pages, 3 figure
Generic chiral superfield model on nonanticommutative N=1/2 superspace
We consider the generic nonanticommutative model of chiral-antichiral
superfields on superspace. The model is formulated in
terms of an arbitrary K\"ahlerian potential, chiral and antichiral
superpotentials and can include the nonanticommutative supersymmetric
sigma-model as a partial case. We study a component structure of the model and
derive the component Lagrangian in an explicit form with all auxiliary fields
contributions. We show that the infinite series in the classical action for
generic nonanticommutative model of chiral-antichiral superfields in D=4
dimensions can be resumed in a compact expression which can be written as a
deformation of standard Zumino's lagrangian and chiral superpotential. Problem
of eliminating the auxiliary fields in the generic model is discussed and the
first perturbative correction to the effective scalar potential is obtained.Comment: 12 pages, LaTeX; text revised and extended, references adde
Gravitational Radiation from a Naked Singularity. II - Even-Parity Perturbation -
A naked singularity occurs in the generic collapse of an inhomogeneous dust
ball. We study the even-parity mode of gravitational waves from a naked
singularity of the Lema\^{\i}tre-Tolman-Bondi spacetime. The wave equations for
gravitational waves are solved by numerical integration using the single null
coordinate. The result implies that the metric perturbation grows when it
approaches the Cauchy horizon and diverges there, although the naked
singularity is not a strong source of even-parity gravitational radiation.
Therefore, the Cauchy horizon in this spacetime should be unstable with respect
to linear even-parity perturbations.Comment: 16 pages, 5 figures, errors and typos corrected, final versio
Thermal conductance of Andreev interferometers
We calculate the thermal conductance of diffusive Andreev
interferometers, which are hybrid loops with one superconducting arm and one
normal-metal arm. The presence of the superconductor suppresses ; however,
unlike a conventional superconductor, does not vanish as the
temperature , but saturates at a finite value that depends on the
resistance of the normal-superconducting interfaces, and their distance from
the path of the temperature gradient. The reduction of is determined
primarily by the suppression of the density of states in the proximity-coupled
normal metal along the path of the temperature gradient. is also a
strongly nonlinear function of the thermal current, as found in recent
experiments.Comment: 5 pages, 4 figure
Paradox of inductionless magnetorotational instability in a Taylor-Couette flow with a helical magnetic field
We consider the magnetorotational instability (MRI) of a hydrodynamically
stable Taylor-Couette flow with a helical external magnetic field in the
inductionless approximation defined by a zero magnetic Prandtl number
(\Pm=0). This leads to a considerable simplification of the problem
eventually containing only hydrodynamic variables. First, we point out that the
energy of any perturbation growing in the presence of magnetic field has to
grow faster without the field. This is a paradox because the base flow is
stable without the magnetic while it is unstable in the presence of a helical
magnetic field without being modified by the latter as it has been found
recently by Hollerbach and Rudiger [Phys. Rev. Lett. 95, 124501 (2005)]. We
revisit this problem by using a Chebyshev collocation method to calculate the
eigenvalue spectrum of the linearized problem. In this way, we confirm that MRI
with helical magnetic field indeed works in the inductionless limit where the
destabilization effect appears as an effective shift of the Rayleigh line.
Second, we integrate the linearized equations in time to study the transient
behavior of small amplitude perturbations, thus showing that the energy
arguments are correct as well. However, there is no real contradiction between
both facts. The linear stability theory predicts the asymptotic development of
an arbitrary small-amplitude perturbation, while the energy stability theory
yields the instant growth rate of any particular perturbation, but it does not
account for the evolution of this perturbation.Comment: 4 pages, 3 figures, submitted to Phys. Rev.
Magnetorotational-type instability in Couette-Taylor flow of a viscoelastic polymer liquid
We describe an instability of viscoelastic Couette-Taylor flow that is
directly analogous to the magnetorotational instability (MRI) in astrophysical
magnetohydrodynamics, with polymer molecules playing the role of magnetic field
lines. By determining the conditions required for the onset of instability and
the properties of the preferred modes, we distinguish it from the centrifugal
and elastic instabilities studied previously. Experimental demonstration and
investigation should be much easier for the viscoelastic instability than for
the MRI in a liquid metal. The analogy holds with the case of a predominantly
toroidal magnetic field such as is expected in an accretion disk and it may be
possible to access a turbulent regime in which many modes are unstable.Comment: 4 pages, 4 figures, to be published in Physical Review Letter
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