4,104 research outputs found
Merger Transitions in Brane--Black-Hole Systems: Criticality, Scaling, and Self-Similarity
We propose a toy model for study merger transitions in a curved spaceime with
an arbitrary number of dimensions. This model includes a bulk N-dimensional
static spherically symmetric black hole and a test D-dimensional brane
interacting with the black hole. The brane is asymptotically flat and allows
O(D-1) group of symmetry. Such a brane--black-hole (BBH) system has two
different phases. The first one is formed by solutions describing a brane
crossing the horizon of the bulk black hole. In this case the internal induced
geometry of the brane describes D-dimensional black hole. The other phase
consists of solutions for branes which do not intersect the horizon and the
induced geometry does not have a horizon. We study a critical solution at the
threshold of the brane-black-hole formation, and the solutions which are close
to it. In particular, we demonstrate, that there exists a striking similarity
of the merger transition, during which the phase of the BBH-system is changed,
both with the Choptuik critical collapse and with the merger transitions in the
higher dimensional caged black-hole--black-string system.Comment: 9 pages 2 figures; additional remarks and references are added at
Section IX "Discussion
Stationary strings near a higher-dimensional rotating black hole
We study stationary string configurations in a space-time of a
higher-dimensional rotating black hole. We demonstrate that the Nambu-Goto
equations for a stationary string in the 5D Myers-Perry metric allow a
separation of variables. We present these equations in the first-order form and
study their properties. We prove that the only stationary string configuration
which crosses the infinite red-shift surface and remains regular there is a
principal Killing string. A worldsheet of such a string is generated by a
principal null geodesic and a timelike at infinity Killing vector field. We
obtain principal Killing string solutions in the Myers-Perry metrics with an
arbitrary number of dimensions. It is shown that due to the interaction of a
string with a rotating black hole there is an angular momentum transfer from
the black hole to the string. We calculate the rate of this transfer in a
spacetime with an arbitrary number of dimensions. This effect slows down the
rotation of the black hole. We discuss possible final stationary configurations
of a rotating black hole interacting with a string.Comment: 13 pages, contains additianal material at the end of Section 8, also
small misprints are correcte
Thermonuclear burn-up in deuterated methane
The thermonuclear burn-up of highly compressed deuterated methane CD is
considered in the spherical geometry. The minimal required values of the
burn-up parameter are determined for various
temperatures and densities . It is shown that thermonuclear burn-up
in becomes possible in practice if its initial density exceeds
. Burn-up in CDT methane
requires significantly ( 100 times) lower compressions. The developed
approach can be used in order to compute the critical burn-up parameters in an
arbitrary deuterium containing fuel
Continuous Self-Similarity Breaking in Critical Collapse
This paper studies near-critical evolution of the spherically symmetric
scalar field configurations close to the continuously self-similar solution.
Using analytic perturbative methods, it is shown that a generic growing
perturbation departs from the critical Roberts solution in a universal way. We
argue that in the course of its evolution, initial continuous self-similarity
of the background is broken into discrete self-similarity with echoing period
, reproducing the symmetries of the critical
Choptuik solution.Comment: RevTeX 3.1, 28 pages, 5 figures; discussion rewritten to clarify
several issue
On the bound state of the antiproton-deuterium-tritium ion
The properties of the weakly-bound state in the ion
are investigated with the use of the results of highly accurate computations.
The hyperfine structure splitting of this ion is investigated. We also evaluate
the life-time of the ion against the nuclear fusion and
discuss a possibility to evaluate the corresponding annihilation rate(s)
Interaction of higher-dimensional rotating black holes with branes
We study interaction of rotating higher dimensional black holes with a brane
in space-times with large extra dimensions. We demonstrate that in a general
case a rotating black hole attached to a brane can loose bulk components of its
angular momenta. A stationary black hole can have only those components of the
angular momenta which are connected with Killing vectors generating
transformations preserving a position of the brane. In a final stationary state
the null Killing vector generating the black hole horizon is tangent to the
brane. We discuss first the interaction of a cosmic string and a domain wall
with the 4D Kerr black hole. We then prove the general result for slowly
rotating higher dimensional black holes interacting with branes. The
characteristic time when a rotating black hole with the gravitational radius
reaches this final stationary state is , where
is the higher dimensional gravitational coupling constant, is the
brane tension, and is the number of extra dimensions.Comment: Version published in Class. Quant. Gra
A not so brief commentary on cosmological entropy bounds
There has been, quite recently, a discussion on how holographic-inspired
bounds might be used to encompass the present-day dark energy and
early-universe inflation into a single paradigm. In the current treatment, we
point out an inconsistency in the proposed framework and then provide a viable
resolution. We also elaborate on some of the implications of this framework and
further motivate the proposed holographic connection. The manuscript ends with
a more speculative note on cosmic time as an emergent (holographically induced)
construct.Comment: 12 pages and Revtex; (v2) reference added and a few cosmetic change
Neural Distributed Autoassociative Memories: A Survey
Introduction. Neural network models of autoassociative, distributed memory
allow storage and retrieval of many items (vectors) where the number of stored
items can exceed the vector dimension (the number of neurons in the network).
This opens the possibility of a sublinear time search (in the number of stored
items) for approximate nearest neighbors among vectors of high dimension. The
purpose of this paper is to review models of autoassociative, distributed
memory that can be naturally implemented by neural networks (mainly with local
learning rules and iterative dynamics based on information locally available to
neurons). Scope. The survey is focused mainly on the networks of Hopfield,
Willshaw and Potts, that have connections between pairs of neurons and operate
on sparse binary vectors. We discuss not only autoassociative memory, but also
the generalization properties of these networks. We also consider neural
networks with higher-order connections and networks with a bipartite graph
structure for non-binary data with linear constraints. Conclusions. In
conclusion we discuss the relations to similarity search, advantages and
drawbacks of these techniques, and topics for further research. An interesting
and still not completely resolved question is whether neural autoassociative
memories can search for approximate nearest neighbors faster than other index
structures for similarity search, in particular for the case of very high
dimensional vectors.Comment: 31 page
Global geometry of two-dimensional charged black holes
The semiclassical geometry of charged black holes is studied in the context
of a two-dimensional dilaton gravity model where effects due to pair-creation
of charged particles can be included in a systematic way. The classical
mass-inflation instability of the Cauchy horizon is amplified and we find that
gravitational collapse of charged matter results in a spacelike singularity
that precludes any extension of the spacetime geometry. At the classical level,
a static solution describing an eternal black hole has timelike singularities
and multiple asymptotic regions. The corresponding semiclassical solution, on
the other hand, has a spacelike singularity and a Penrose diagram like that of
an electrically neutral black hole. Extremal black holes are destabilized by
pair-creation of charged particles. There is a maximally charged solution for a
given black hole mass but the corresponding geometry is not extremal. Our
numerical data exhibits critical behavior at the threshold for black hole
formation.Comment: REVTeX, 13 pages, 12 figures; Reference adde
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