4,029 research outputs found
Applications of hidden symmetries to black hole physics
This work is a brief review of applications of hidden symmetries to black
hole physics. Symmetry is one of the most important concepts of the science. In
physics and mathematics the symmetry allows one to simplify a problem, and
often to make it solvable. According to the Noether theorem symmetries are
responsible for conservation laws. Besides evident (explicit) spacetime
symmetries, responsible for conservation of energy, momentum, and angular
momentum of a system, there also exist what is called hidden symmetries, which
are connected with higher order in momentum integrals of motion. A remarkable
fact is that black holes in four and higher dimensions always possess a set
(`tower') of explicit and hidden symmetries which make the equations of motion
of particles and light completely integrable. The paper gives a general review
of the recently obtained results. The main focus is on understanding why at all
black holes have something (symmetry) to hide.Comment: This is an extended version of the talks at NEB-14 conference
(June,Ioannina,Greece) and JGRG20 meeting (September, Kyoto, Japan
Energy flux through the horizon in the black hole-domain wall systems
We study various configurations in which a domain wall (or cosmic string),
described by the Nambu-Goto action, is embedded in a background space-time of a
black hole in and higher dimensional models. We calculate energy fluxes
through the black hole horizon. In the simplest case, when a static domain wall
enters the horizon of a static black hole perperdicularly, the energy flux is
zero. In more complicated situations, where parameters which describe the
domain wall surface are time and position dependent, the flux is non-vanishing
is principle. These results are of importance in various conventional
cosmological models which accommodate the existence of domain walls and strings
and also in brane world scenarios.Comment: references added, accepted for publication in JHE
Capillary instability in nanowire geometries
The vapor-liquid-solid (VLS) mechanism has been applied extensively as a
framework for growing single-crystal semiconductor nanowires for applications
spanning optoelectronic, sensor and energy-related technologies. Recent
experiments have demonstrated that subtle changes in VLS growth conditions
produce a diversity of nanowire morphologies, and result in intricate kinked
structures that may yield novel properties. These observations have motivated
modeling studies that have linked kinking phenomena to processes at the triple
line between vapor, liquid and solid phases that cause spontaneous "tilting" of
the growth direction. Here we present atomistic simulations and theoretical
analyses that reveal a tilting instability that is intrinsic to nanowire
geometries, even in the absence of pronounced anisotropies in solid-liquid
interface properties. The analysis produces a very simple conclusion: the
transition between axisymmetric and tilted triple lines is shown to occur when
the triple line geometry satisfies Young's force-balance condition. The
intrinsic nature of the instability may have broad implications for the design
of experimental strategies for controlled growth of crystalline nanowires with
complex geometries.Comment: 10 pages, 5 figure
Black hole entropy without brick walls
The properties of the thermal radiation are discussed by using the new
equation of state density motivated by the generalized uncertainty relation in
the quantum gravity. There is no burst at the last stage of the emission of a
Schwarzshild black hole. When the new equation of state density is utilized to
investigate the entropy of a scalar field outside the horizon of a static black
hole, the divergence appearing in the brick wall model is removed, without any
cutoff. The entropy proportional to the horizon area is derived from the
contribution of the vicinity of the horizon.Comment: 7 page
Interaction of a brane with a moving bulk black hole
We study the interaction of an n-dimensional topological defect (n-brane)
described by the Nambu-Goto action with a higher-dimensional Schwarzschild
black hole moving in the bulk spacetime. We derive the general form of the
perturbation equations for an n-brane in the weak field approximation and solve
them analytically in the most interesting cases. We specially analyze
applications to brane world models. We calculate the induced geometry on the
brane generated by a moving black hole. From the point of view of a brane
observer, this geometry can be obtained by solving (n+1)-dimensional Einstein's
equations with a non-vanishing right hand side. We calculate the effective
stress-energy tensor corresponding to this `shadow-matter'. We explicitly show
that there exist regions on the brane where a brane observer sees an apparent
violation of energy conditions. We also study the deflection of light
propagating in the region of influence of this `shadow matter'.Comment: version accepted for publication in Phys. Rev.
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.
Stationary strings and branes in the higher-dimensional Kerr-NUT-(A)dS spacetimes
We demonstrate complete integrability of the Nambu-Goto equations for a
stationary string in the general Kerr-NUT-(A)dS spacetime describing the
higher-dimensional rotating black hole. The stationary string in D dimensions
is generated by a 1-parameter family of Killing trajectories and the problem of
finding a string configuration reduces to a problem of finding a geodesic line
in an effective (D-1)-dimensional space. Resulting integrability of this
geodesic problem is connected with the existence of hidden symmetries which are
inherited from the black hole background. In a spacetime with p mutually
commuting Killing vectors it is possible to introduce a concept of a
-brane, that is a p-brane with the worldvolume generated by these fields
and a 1-dimensional curve. We discuss integrability of such -branes in the
Kerr-NUT-(A)dS spacetime.Comment: 8 pages, no figure
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