1,300 research outputs found
Observations of electron gyroharmonic waves and the structure of the Io torus
Narrow-banded emissions were observed by the Planetary Radio Astronomy experiment on the Voyager 1 spacecraft as it traversed the Io plasma torus. These waves occur between harmonics of the electron gyrofrequency and are the Jovian analogue of electrostatic emissions observed and theoretically studied for the terrestrial magnetosphere. The observed frequencies always include the component near the upper hybrid resonant frequency, (fuhr) but the distribution of the other observed emissions varies in a systematic way with position in the torus. A refined model of the electron density variation, based on identification of the fuhr line, is included. Spectra of the observed waves are analyzed in terms of the linear instability of an electron distribution function consisting of isotropic cold electrons and hot losscone electrons. The positioning of the observed auxiliary harmonics with respect to fuhr is shown to be an indicator of the cold to hot temperature ratio. It is concluded that this ratio increases systematically by an overall factor of perhaps 4 or 5 between the inner and outer portions of the torus
An Exact Black Hole Entropy Bound
We show that a Rademacher expansion can be used to establish an exact bound
for the entropy of black holes within a conformal field theory framework. This
convergent expansion includes all subleading corrections to the
Bekenstein-Hawking term.Comment: 6 pages, Latex, v2 minor re-wording, additional reference, to appear
in Phyical Review D (title changed in journal
Topological Modes in Dual Lattice Models
Lattice gauge theory with gauge group is reconsidered in four
dimensions on a simplicial complex . One finds that the dual theory,
formulated on the dual block complex , contains topological modes
which are in correspondence with the cohomology group ,
in addition to the usual dynamical link variables. This is a general phenomenon
in all models with single plaquette based actions; the action of the dual
theory becomes twisted with a field representing the above cohomology class. A
similar observation is made about the dual version of the three dimensional
Ising model. The importance of distinct topological sectors is confirmed
numerically in the two dimensional Ising model where they are parameterized by
.Comment: 10 pages, DIAS 94-3
A Closed Contour of Integration in Regge Calculus
The analytic structure of the Regge action on a cone in dimensions over a
boundary of arbitrary topology is determined in simplicial minisuperspace. The
minisuperspace is defined by the assignment of a single internal edge length to
all 1-simplices emanating from the cone vertex, and a single boundary edge
length to all 1-simplices lying on the boundary. The Regge action is analyzed
in the space of complex edge lengths, and it is shown that there are three
finite branch points in this complex plane. A closed contour of integration
encircling the branch points is shown to yield a convergent real wave function.
This closed contour can be deformed to a steepest descent contour for all sizes
of the bounding universe. In general, the contour yields an oscillating wave
function for universes of size greater than a critical value which depends on
the topology of the bounding universe. For values less than the critical value
the wave function exhibits exponential behaviour. It is shown that the critical
value is positive for spherical topology in arbitrary dimensions. In three
dimensions we compute the critical value for a boundary universe of arbitrary
genus, while in four and five dimensions we study examples of product manifolds
and connected sums.Comment: 16 pages, Latex, To appear in Gen. Rel. Gra
Interpolating gauge fixing for Chern-Simons theory
Chern-Simons theory is analyzed with a gauge-fixing which allows to discuss
the Landau gauge and the light-cone gauge at the same time.Comment: 11 pages, Report TUW-93-2
BTZ black holes and the near-horizon geometry of higher-dimensional black holes
We investigate the connection between the BTZ black holes and the
near-horizon geometry of higher-dimensional black holes. Under mild conditions,
we show that (i) if a black hole has a global structure of the type of the
non-extremal Reissner-Nordstrom black holes, its near-horizon geometry is
times a sphere, and further (ii) if such a black hole is obtained from
a boosted black string by dimensional reduction, the near-horizon geometry of
the latter contains a BTZ black hole. Because of these facts, the calculation
of the Bekenstein-Hawking entropy and the absorption cross-sections of scalar
fields is essentially reduced to the corresponding calculation in the BTZ
geometry under appropriate conditions. This holds even if the geometry is not
supersymmetric in the extremal limit. Several examples are discussed. We also
discuss some generalizations to geometries which do not have near the
horizon.Comment: 19 pages, LaTex, (v2) a comment on black holes with 2 and 3 charges
added, (v3) some phrases made more precise, references added, minor changes;
version to appear in Phys. Rev.
Cardy-Verlinde Formula and AdS Black Holes
In a recent paper hep-th/0008140 by E. Verlinde, an interesting formula has
been put forward, which relates the entropy of a conformal formal field in
arbitrary dimensions to its total energy and Casimir energy. This formula has
been shown to hold for the conformal field theories that have AdS duals in the
cases of AdS Schwarzschild black holes and AdS Kerr black holes. In this paper
we further check this formula with various black holes with AdS asymptotics.
For the hyperbolic AdS black holes, the Cardy-Verlinde formula is found to hold
if we choose the ``massless'' black hole as the ground state, but in this case,
the Casimir energy is negative. For the AdS Reissner-Nordstr\"om black holes in
arbitrary dimensions and charged black holes in D=5, D=4, and D=7 maximally
supersymmetric gauged supergravities, the Cardy-Verlinde formula holds as well,
but a proper internal energy which corresponds to the mass of supersymmetric
backgrounds must be subtracted from the total energy. It is failed to rewrite
the entropy of corresponding conformal field theories in terms of the
Cardy-Verlinde formula for the AdS black holes in the Lovelock gravity.Comment: 18 pages, latex, no figures, discussions on the charged AdS black
holes change
Greybody factor for the BTZ black hole and a 5D black hole
We study the 5D black holes in the type IIB superstring theory compactified
on . Far from horizon, we have flat space-time. Near horizon,
we have . We calculate the
greybody factor of a minimally coupled scalar by replacing the original
geometry() by . In the
low-energy scattering, it turns out that the result agrees with the greybody
factor of the 5D black hole (or D1 + D5 branes)in the dilute gas approximation.
This confirms that the -theory() contains the
essential information about the bulk 5D black holes.Comment: some discussions are added, 15 Pages, No figure, RevTe
Dynamical Behavior of the BTZ Black Hole
We study the dynamical behavior of the BTZ (Banados-Teitelboim-Zanelli) black
hole with the low-energy string effective action. The perturbation analysis
around the BTZ black hole reveals a mixing between the dilaton and other
fields. Introducing the new gauge (dilaton gauge), we disentangle this mixing
completely and obtain one decoupled dilaton equation. We obtain the decay rate
of BTZ black hole.Comment: minor typhographical corrections, ReVTeX, 9 pages with no figure
The renormalization group and spontaneous compactification of a higher-dimensional scalar field theory in curved spacetime
The renormalization group (RG) is used to study the asymptotically free
-theory in curved spacetime. Several forms of the RG equations for
the effective potential are formulated. By solving these equations we obtain
the one-loop effective potential as well as its explicit forms in the case of
strong gravitational fields and strong scalar fields. Using zeta function
techniques, the one-loop and corresponding RG improved vacuum energies are
found for the Kaluza-Klein backgrounds and . They are given in terms of exponentially convergent series, appropriate
for numerical calculations. A study of these vacuum energies as a function of
compactification lengths and other couplings shows that spontaneous
compactification can be qualitatively different when the RG improved energy is
used.Comment: LaTeX, 15 pages, 4 figure
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