10,570 research outputs found
Dyonic dilaton black holes
The properties of static spherically symmetric black holes, which are both
electrically and magnetically charged, and which are coupled to the dilaton in
the presence of a cosmological constant, Lambda, are considered. It is shown
that apart from the Reissner-Nordstrom-de Sitter solution with constant
dilaton, such solutions do not exist if Lambda > 0 (in arbitrary spacetime
dimension >=4 ). However, asymptotically anti-de Sitter dyonic black hole
solutions with a non-trivial dilaton do exist if Lambda < 0. Both these
solutions and the asymptotically flat (Lambda = 0) solutions are studied
numerically for arbitrary values of the dilaton coupling parameter, g_0, in
four dimensions. The asymptotically flat solutions are found to exhibit two
horizons if g_0 = 0, 1, \sqrt{3}, \sqrt{6}, ..., \sqrt{n(n+1)/2},..., and one
horizon otherwise. For asymptotically anti-de Sitter solutions the result is
similar, but the corresponding values of g_0 are altered in a non-linear
fashion which depends on Lambda and the mass and charges of the black holes.
All dyonic solutions with Lambda <= 0 are found to have zero Hawking
temperature in the extreme limit, however, regardless of the value of g_0.Comment: 24 pages, phyzzx, epsf, 7 in-text figures. Small addition to
introduction, and a few extra reference
Universal properties of the near-horizon optical geometry
We make use of the fact that the optical geometry near a static
non-degenerate Killing horizon is asymptotically hyperbolic to investigate
universal features of black hole physics. We show how the Gauss-Bonnet theorem
allows certain lensing scenarios to be ruled in or out. We find rates for the
loss of scalar, vector and fermionic `hair' as objects fall quasi- statically
towards the horizon. In the process we find the Lienard-Wiechert potential for
hyperbolic space and calculate the force between electrons mediated by
neutrinos, extending the flat space result of Feinberg and Sucher. We use the
enhanced conformal symmetry of the Schwarzschild and Reissner-Nordstrom
backgrounds to re-derive the electrostatic field due to a point charge in a
simple fashion
Collapsing Shells and the Isoperimetric Inequality for Black Holes
Recent results of Trudinger on Isoperimetric Inequalities for non-convex
bodies are applied to the gravitational collapse of a lightlike shell of matter
to form a black hole. Using some integral identities for co-dimension two
surfaces in Minkowski spacetime, the area of the apparent horizon is shown
to be bounded above in terms of the mass by the , which is
consistent with the Cosmic Censorship Hypothesis. The results hold in four
spacetime dimensions and above.Comment: 16 pages plain TE
Statistical Mechanics of Charged Particles in Einstein-Maxwell-Scalar Theory
We consider an -body system of charged particle coupled to gravitational,
electromagnetic, and scalar fields. The metric on moduli space for the system
can be considered if a relation among the charges and mass is satisfied, which
includes the BPS relation for monopoles and the extreme condition for charged
black holes. Using the metric on moduli space in the long distance
approximation, we study the statistical mechanics of the charged particles at
low velocities. The partition function is evaluated as the leading order of the
large expansion, where is the spatial dimension of the system and will
be substituted finally as .Comment: 11 pages, RevTeX3.
Charged Dilaton Black Holes with a Cosmological Constant
The properties of static spherically symmetric black holes, which are either
electrically or magnetically charged, and which are coupled to the dilaton in
the presence of a cosmological constant, are considered. It is shown that such
solutions do not exist if the cosmological constant is positive (in arbitrary
spacetime dimension >= 4). However, asymptotically anti-de Sitter black hole
solutions with a single horizon do exist if the cosmological constant is
negative. These solutions are studied numerically in four dimensions and the
thermodynamic properties of the solutions are derived. The extreme solutions
are found to have zero entropy and infinite temperature for all non-zero values
of the dilaton coupling constant.Comment: 12 pages, epsf, phyzzx, 4 in-text figures incl. (minor typos fixed, 1
reference added
D-string on near horizon geometries and infinite conformal symmetry
We show that the symmetries of effective D-string actions in constant dilaton
backgrounds are directly related to homothetic motions of the background
metric. In presence of such motions, there are infinitely many nonlinearly
realized rigid symmetries forming a loop (or loop like) algebra. Near horizon
(AdS) D3 and D1+D5 backgrounds are discussed in detail and shown to provide 2d
interacting field theories with infinite conformal symmetry.Comment: 5 pages, revtex, no figures; symmetry transformations for BI action
added, coupling of D-string to RR 2-form in D1-D5 background corrected; final
version, to appear in Phys. Rev. Let
Topology, Entropy and Witten Index of Dilaton Black Holes
We have found that for extreme dilaton black holes an inner boundary must be
introduced in addition to the outer boundary to give an integer value to the
Euler number. The resulting manifolds have (if one identifies imaginary time)
topology and Euler number in contrast to
the non-extreme case with . The entropy of extreme dilaton black
holes is already known to be zero. We include a review of some recent ideas due
to Hawking on the Reissner-Nordstr\"om case. By regarding all extreme black
holes as having an inner boundary, we conclude that the entropy of {\sl all}
extreme black holes, including black holes, vanishes. We discuss the
relevance of this to the vanishing of quantum corrections and the idea that the
functional integral for extreme holes gives a Witten Index. We have studied
also the topology of ``moduli space'' of multi black holes. The quantum
mechanics on black hole moduli spaces is expected to be supersymmetric despite
the fact that they are not HyperK\"ahler since the corresponding geometry has
torsion unlike the BPS monopole case. Finally, we describe the possibility of
extreme black hole fission for states with an energy gap. The energy released,
as a proportion of the initial rest mass, during the decay of an
electro-magnetic black hole is 300 times greater than that released by the
fission of an nucleus.Comment: 51 pages, 4 figures, LaTeX. Considerably extended version. New
sections include discussion of the Witten index, topology of the moduli
space, black hole sigma model, and black hole fission with huge energy
releas
More about Birkhoff's Invariant and Thorne's Hoop Conjecture for Horizons
A recent precise formulation of the hoop conjecture in four spacetime
dimensions is that the Birkhoff invariant (the least maximal length of
any sweepout or foliation by circles) of an apparent horizon of energy and
area should satisfy . This conjecture together with the
Cosmic Censorship or Isoperimetric inequality implies that the length of
the shortest non-trivial closed geodesic satisfies . We have
tested these conjectures on the horizons of all four-charged rotating black
hole solutions of ungauged supergravity theories and find that they always
hold. They continue to hold in the the presence of a negative cosmological
constant, and for multi-charged rotating solutions in gauged supergravity.
Surprisingly, they also hold for the Ernst-Wild static black holes immersed in
a magnetic field, which are asymptotic to the Melvin solution. In five
spacetime dimensions we define as the least maximal area of all
sweepouts of the horizon by two-dimensional tori, and find in all cases
examined that , which we conjecture holds
quiet generally for apparent horizons. In even spacetime dimensions ,
we find that for sweepouts by the product , is
bounded from above by a certain dimension-dependent multiple of the energy .
We also find that is bounded from above by a certain
dimension-dependent multiple of the horizon area . Finally, we show that
is bounded from above by a certain dimension-dependent multiple of
the energy, for all Kerr-AdS black holes.Comment: 25 page
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
Black Hole Geometries in Noncommutative String Theory
We obtain a generalized Schwarzschild (GS-) and a generalized
Reissner-Nordstrom (GRN-) black hole geometries in (3+1)-dimensions, in a
noncommutative string theory. In particular, we consider an effective theory of
gravity on a curved -brane in presence of an electromagnetic (EM-) field.
Two different length scales, inherent in its noncommutative counter-part, are
exploited to obtain a theory of effective gravity coupled to an U(1)
noncommutative gauge theory to all orders in . It is shown that the
GRN-black hole geometry, in the Planckian regime, reduces to the GS-black hole.
However in the classical regime it may be seen to govern both
Reissner-Nordstrom and Schwarzschild geometries independently. The emerging
notion of 2D black holes evident in the frame-work are analyzed. It is argued
that the -string in the theory may be described by the near horizon 2D black
hole geometry, in the gravity decoupling limit. Finally, our analysis explains
the nature of the effective force derived from the nonlinear EM-field and
accounts for the Hawking radiation phenomenon in the formalism.Comment: 30 pages, 2 figure
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