67,549 research outputs found
Perturbations and absorption cross-section of infinite-radius black rings
We study scalar field perturbations on the background of non-supersymmetric
black rings and of supersymmetric black rings. In the infinite-radius limit of
these geometries, we are able to separate the wave equation, and to study wave
phenomena in its vicinities. In this limit, we show that (i) both geometries
are stable against scalar field perturbations, (ii) the absorption
cross-section for scalar fields is equal to the area of the event horizon in
the supersymmetric case, and proportional to it in the non-supersymmetric
situation.Comment: ReVTeX4. 15 pages, 3 figures. References added. Published versio
AC Response of Thin Film Superconductors at Various Temperatures and Magnetic Fields
The basic theory of the linear and nonlinear ac susceptibilities of type-II
superconductors is outlined for various geometries, e.g. circular and elliptic
disks, rings, and strips of thin films or of thicker platelets in a
perpendicular magnetic field. It is shown how the linear susceptibility depends
on the linear complex resistivity or on the complex penetration depth, and the
nonlinear susceptibility on the nonlinear dependence of the electric field on
the current density and magnetic induction. The dependence of these
constitutive laws on the temperature and on various material properties like
pinning forces, pinning energies, structural defects, and granularity, leads to
an implicit dependence of the ac susceptibility on these parameters.Comment: Latex file and 3 postscript figures, gives 13 pages text with figures
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Constructing near-horizon geometries in supergravities with hidden symmetry
We consider the classification of near-horizon geometries in a general
two-derivative theory of gravity coupled to abelian gauge fields and uncharged
scalars in four and five dimensions, with one and two commuting rotational
symmetries respectively. Assuming that the theory of gravity reduces to a 3d
non-linear sigma model (as is typically the case for ungauged supergravities),
we show that the functional form of any such near-horizon geometry may be
determined. As an example we apply this to five dimensional minimal
supergravity. We also construct an example of a five parameter near-horizon
geometry solution to this theory with S^1 X S^2 horizon topology. We discuss
its relation to the near-horizon geometries of the yet to be constructed
extremal black rings with both electric and dipole charges.Comment: Latex, 30 pages. v2: discussion in section 5 modified and improved,
other minor changes, references adde
Polynomial Rings and Topological Strings
An overview is given of the construction of a differential polynomial ring of
functions on the moduli space of Calabi-Yau threefolds. These rings coincide
with the rings of quasi modular forms for geometries with duality groups for
which these are known. They provide a generalization thereof otherwise. Higher
genus topological string amplitudes can be expressed in terms of the generators
of this ring giving them a global description in the moduli space. An action of
a duality exchanging large volume and conifold loci in moduli space is
discussed. The connection to quasi modular forms is illustrated by the local
P^2 geometry and its mirror, the generalization is extended to several compact
geometries with one-dimensional moduli spaces.Comment: 10 pages, 2 figures, contribution to the proceedings of the
String-Math 2013 conferenc
Phase light curves for extrasolar Jupiters and Saturns
We predict how a remote observer would see the brightness variations of giant
planets similar to Jupiter and Saturn as they orbit their central stars. We
model the geometry of Jupiter, Saturn and Saturn's rings for varying orbital
and viewing parameters. Scattering properties for the planets and rings at
wavelenghts 0.6-0.7 microns follow Pioneer and Voyager observations, namely,
planets are forward scattering and rings are backward scattering. Images of the
planet with or without rings are simulated and used to calculate the
disk-averaged luminosity varying along the orbit, that is, a light curve is
generated. We find that the different scattering properties of Jupiter and
Saturn (without rings) make a substantial difference in the shape of their
light curves. Saturn-size rings increase the apparent luminosity of the planet
by a factor of 2-3 for a wide range of geometries. Rings produce asymmetric
light curves that are distinct from the light curve of the planet without
rings. If radial velocity data are available for the planet, the effect of the
ring on the light curve can be distinguished from effects due to orbital
eccentricity. Non-ringed planets on eccentric orbits produce light curves with
maxima shifted relative to the position of the maximum planet's phase. Given
radial velocity data, the amount of the shift restricts the planet's unknown
orbital inclination and therefore its mass. Combination of radial velocity data
and a light curve for a non-ringed planet on an eccentric orbit can also be
used to constrain the surface scattering properties of the planet. To summarize
our results for the detectability of exoplanets in reflected light, we present
a chart of light curve amplitudes of non-ringed planets for different
eccentricities, inclinations, and the viewing azimuthal angles of the observer.Comment: 40 pages, 13 figures, submitted to Ap.
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