101 research outputs found
Analyticity Properties of Graham-Witten Anomalies
Analytic properties of Graham-Witten anomalies are considered. Weyl anomalies
according to their analytic properties are of type A (coming from
-singularities in correlators of several energy-momentum tensors) or of
type B (originating in counterterms which depend logarithmically on a mass
scale). It is argued that all Graham-Witten anomalies can be divided into 2
groups: internal and external, and that all external anomalies are of type B,
whereas among internal anomalies there is one term of type A and all the rest
are of type B. This argument is checked explicitly for the case of a free
scalar field in a 6-dimensional space with a 2-dimensional submanifold.Comment: 2 typos correcte
Dynamical vs. Auxiliary Fields in Gravitational Waves around a Black Hole
The auxiliary/dynamic decoupling method of hep-th/0609001 applies to
perturbations of any co-homogeneity 1 background (such as a spherically
symmetric space-time or a homogeneous cosmology). Here it is applied to compute
the perturbations around a Schwarzschild black hole in an arbitrary dimension.
The method provides a clear insight for the existence of master equations. The
computation is straightforward, coincides with previous results of
Regge-Wheeler, Zerilli and Kodama-Ishibashi but does not require any ingenuity
in either the definition of variables or in fixing the gauge. We note that the
method's emergent master fields are canonically conjugate to the standard ones.
In addition, our action approach yields the auxiliary sectors.Comment: 26 page
High and Low Dimensions in The Black Hole Negative Mode
The negative mode of the Schwarzschild black hole is central to Euclidean
quantum gravity around hot flat space and for the Gregory-Laflamme black string
instability. We analyze the eigenvalue as a function of space-time dimension by
constructing two perturbative expansions: one for large d and the other for
small d-3, and determining as many coefficients as we are able to compute
analytically. Joining the two expansions we obtain an interpolating rational
function accurate to better than 2% through the whole range of dimensions
including d=4.Comment: 17 pages, 4 figures. v2: added reference. v3: published versio
Auger Spectroscopy of Hydrogenated Diamond Surfaces
An energy shift and a change of the line shape of the carbon core-valence-valence Auger spectra are observed for diamond surfaces after their exposure to an electron beam, or annealing at temperatures higher then 950 C. The effect is studied for both natural diamond crystals and chemical-vapor-deposited diamond films. A theoretical model is proposed for Auger spectra of hydrogenated diamond surfaces. The observed changes of the carbon Auger line shape are shown to be related to the redistribution of the valence-band local density of states caused by the hydrogen desorption from the surface. One-electron calculation of Auger spectra of diamond surfaces with various hydrogen coverages are presented. They are based on self-consistent wave functions and matrix elements calculated in the framework of the local-density approximation and the self-consistent linear muffin-tin orbital method with static core-hole effects taken into account. The major features of experimental spectra are explained
Biexciton oscillator strength
Our goal is to provide a physical understanding of the elementary coupling
between photon and biexciton and to derive the physical characteristics of the
biexciton oscillator strength, following the procedure we used for trion.
Instead of the more standard two-photon absorption, this work concentrates on
molecular biexciton created by photon absorption in an exciton gas. We first
determine the appropriate set of coordinates in real and momentum spaces to
describe one biexciton as two interacting excitons. We then turn to second
quantization and introduce the "Fourier transform in the exciton sense" of the
biexciton wave function which is the relevant quantity for oscillator strength.
We find that, like for trion, the oscillator strength for the formation of one
biexciton out of one photon plus a \emph{single} exciton is extremely small: it
is one biexciton volume divided by one sample volume smaller than the exciton
oscillator strength. However, due to their quantum nature, trion and biexciton
have absorption lines which behave quite differently. Electrons and trions are
fermionic particles impossible to pile up all at the same energy. This would
make the weak trion line spread with electron density, the peak structure only
coming from singular many-body effects. By contrast, the bosonic nature of
exciton and biexciton makes the biexciton peak mainly rise with exciton
density, this rise being simply linear if we forget many-body effects between
the photocreated exciton and the excitons present in the sample
Fast detector of the ellipticity of infrared and terahertz radiation based on HgTe quantum well structures
We report a fast, room temperature detection scheme for the polarization
ellipticity of laser radiation, with a bandwidth that stretches from the
infrared to the terahertz range. The device consists of two elements, one in
front of the other, that detect the polarization ellipticity and the azimuthal
angle of the ellipse. The elements respectively utilise the circular
photogalvanic effect in a narrow gap semiconductor and the linear photogalvanic
effect in a bulk piezoelectric semiconductor. For the former we characterized
both a HgTe quantum well and bulk Te, and for the latter, bulk GaAs. In
contrast with optical methods our device is an easy to handle all-electric
approach, which we demonstrated by applying a large number of different lasers
from low power, continuous wave systems to high power, pulsed sources.Comment: 7 pages, 5 figure
Negative Electron Affinity Effect on the Surface of Chemical Vapor Deposited Diamond Polycrystalline Films
Strong negative electron affinity effects have been observed on the surface of as-grown chemical vapor deposited diamond using Secondary Electron Emission. The test samples were randomly oriented and the surface was terminated with hydrogen. The effect appears as an intensive peak in the low energy part of the spectrum of the electron energy distribution and may be described in the model of effective negative electron affinity
Particle Production near an AdS Crunch
We numerically study the dual field theory evolution of five-dimensional
asymptotically anti-de Sitter solutions of supergravity that develop
cosmological singularities. The dual theory is an unstable deformation of the N
= 4 gauge theory on R S3, and the big crunch singularity in the bulk
occurs when a boundary scalar field runs to infinity. Consistent quantum
evolution requires one imposes boundary conditions at infinity. Modeling these
by a steep regularization of the scalar potential, we find that when an
initially nearly homogeneous wavepacket rolls down the potential, most of the
potential energy of the initial configuration is converted into gradient energy
during the first oscillation of the field. This indicates there is no
transition from a big crunch to a big bang in the bulk for dual boundary
conditions of this kind.Comment: 20 pages, 6 figure
One-Dimensional Approximation of Viscous Flows
Attention has been paid to the similarity and duality between the
Gregory-Laflamme instability of black strings and the Rayleigh-Plateau
instability of extended fluids. In this paper, we derive a set of simple
(1+1)-dimensional equations from the Navier-Stokes equations describing thin
flows of (non-relativistic and incompressible) viscous fluids. This
formulation, a generalization of the theory of drop formation by Eggers and his
collaborators, would make it possible to examine the final fate of
Rayleigh-Plateau instability, its dimensional dependence, and possible
self-similar behaviors before and after the drop formation, in the context of
fluid/gravity correspondence.Comment: 17 pages, 3 figures; v2: refs & comments adde
Black Brane Viscosity and the Gregory-Laflamme Instability
We study long wavelength perturbations of neutral black p-branes in
asymptotically flat space and show that, as anticipated in the blackfold
approach, solutions of the relativistic hydrodynamic equations for an effective
p+1-dimensional fluid yield solutions to the vacuum Einstein equations in a
derivative expansion. Going beyond the perfect fluid approximation, we compute
the effective shear and bulk viscosities of the black brane. The values we
obtain saturate generic bounds. Sound waves in the effective fluid are
unstable, and have been previously related to the Gregory-Laflamme instability
of black p-branes. By including the damping effect of the viscosity in the
unstable sound waves, we obtain a remarkably good and simple approximation to
the dispersion relation of the Gregory-Laflamme modes, whose accuracy increases
with the number of transverse dimensions. We propose an exact limiting form as
the number of dimensions tends to infinity.Comment: 16 pages, 3 figures. v2: minor corrections and refs adde
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