13,048 research outputs found
The holographic RG flow in a field theory on a curved background
As shown by Freedman, Gubser, Pilch and Warner, the RG flow in
super-Yang-Mills theory broken to an theory by the addition of a
mass term can be described in terms of a supersymmetric domain wall solution in
five-dimensional gauged supergravity. The FGPW flow is an example
of a holographic RG flow in a field theory on a flat background. Here we put
the field theory studied by Freedman, Gubser, Pilch and Warner on a curved
background, and we construct the supersymmetric domain wall solution
which describes the RG flow in this field theory. This solution is a curved
(non Ricci flat) domain wall solution. This example demonstrates that
holographic RG flows in supersymmetric field theories on a curved
background can be described in terms of curved supersymmetric domain wall
solutions.Comment: 14 pages, LaTe
Bent-Double Radio Sources as Probes of Intergalactic Gas
As the most common environment in the universe, groups of galaxies are likely
to contain a significant fraction of the missing baryons in the form of
intergalactic gas. The density of this gas is an important factor in whether
ram pressure stripping and strangulation affect the evolution of galaxies in
these systems. We present a method for measuring the density of intergalactic
gas using bent-double radio sources that is independent of temperature, making
it complementary to current absorption line measurements. We use this method to
probe intergalactic gas in two different environments: inside a small group of
galaxies as well as outside of a larger group at a 2 Mpc radius and measure
total gas densities of and per cubic centimeter (random and systematic
errors) respectively. We use X-ray data to place an upper limit of K on the temperature of the intragroup gas in the small group.Comment: 6 pages, 1 figure, accepted for publication in Ap
Ocorrência da antracnose em Stylosanthes spp. no Acre e comportamento de material genético introduzido em relação ao agente causal (colletotrichum gloeosporioides).
Em 1980, uma epifitotia da antracnose do Stylosanthes, causada pelo fungo Collettottrichum gloeosporioides (penz.) Saac., foi observada em pastagens e áreas experimentais do Estado do Acre. Os sintomas caracterÃsticos da doença são descritos. Inoculação de plântulas de Stylosanthes spp. a partir de culturas puras do fungo proporcionou o aparecimento do mesmos sintomas após 15 dias. Oito gemoplasmas de duas espécies de Stylosanthes spp., S. guayanensis e S. capitata, foram avaliados no campo em duas épocas distintas. S. guayanensis mostrou-se mais suscetÃvel que S. capitata. O isolado do fungo foi também capaz de produzir sintomas em S. humilis. As condições de pastejo prevalentes parecem ter contribuÃdo para aumentar a vulnerabilidade de S. guayanensis cv. Cook à doença
Automatic speaker segmentation using multiple features and distance measures: a comparison of three approaches
This paper addresses the problem of unsupervised speaker change detection. Three systems based on the Bayesian Information Criterion (BIC) are tested. The first system investigates the AudioSpectrumCentroid and the AudioWaveformEnvelope features, implements a dynamic thresholding followed by a fusion scheme, and finally applies BIC. The second method is a real-time one that uses a metric-based approach employing the line spectral pairs and the BIC to validate a potential speaker change point. The third method consists of three modules. In the first module, a measure based on second-order statistics is used; in the second module, the Euclidean distance and T2 Hotelling statistic are applied; and in the third module, the BIC is utilized. The experiments are carried out on a dataset created by concatenating speakers from the TIMIT database, that is referred to as the TIMIT data set. A comparison between the performance of the three systems is made based on t-statistics
Eccentric binary black-hole mergers: The transition from inspiral to plunge in general relativity
We study the transition from inspiral to plunge in general relativity by
computing gravitational waveforms of non-spinning, equal-mass black-hole
binaries. We consider three sequences of simulations, starting with a
quasi-circular inspiral completing 1.5, 2.3 and 9.6 orbits, respectively, prior
to coalescence of the holes. For each sequence, the binding energy of the
system is kept constant and the orbital angular momentum is progressively
reduced, producing orbits of increasing eccentricity and eventually a head-on
collision. We analyze in detail the radiation of energy and angular momentum in
gravitational waves, the contribution of different multipolar components and
the final spin of the remnant. We find that the motion transitions from
inspiral to plunge when the orbital angular momentum L=L_crit is about 0.8M^2.
For L<L_crit the radiated energy drops very rapidly. Orbits with L of about
L_crit produce our largest dimensionless Kerr parameter for the remnant,
j=J/M^2=0.724. Generalizing a model recently proposed by Buonanno, Kidder and
Lehner to eccentric binaries, we conjecture that (1) j=0.724 is the maximal
Kerr parameter that can be obtained by any merger of non-spinning holes, and
(2) no binary merger (even if the binary members are extremal Kerr black holes
with spins aligned to the orbital angular momentum, and the inspiral is highly
eccentric) can violate the cosmic censorship conjecture.Comment: Added sequence of long inspirals to the study. To match published
versio
Classical instability of Kerr-AdS black holes and the issue of final state
It is now established that small Kerr-Anti-de Sitter (Kerr-AdS) black holes
are unstable against scalar perturbations, via superradiant amplification
mechanism. We show that small Kerr-AdS black holes are also unstable against
gravitational perturbations and we compute the features of this instability. We
also describe with great detail the evolution of this instability. In
particular, we identify its endpoint state. It corresponds to a Kerr-AdS black
hole whose boundary is an Einstein universe rotating with the light velocity.
This black hole is expected to be slightly oblate and to co-exist in
equilibrium with a certain amount of outside radiation.Comment: 11 pages, RevTex4. v2: small typos corrected. Version to appear in
Phys. Rev.
Gravitational waves from extreme mass-ratio inspirals in Dynamical Chern-Simons gravity
Dynamical Chern-Simons gravity is an interesting extension of General
Relativity, which finds its way in many different contexts, including string
theory, cosmological settings and loop quantum gravity. In this theory, the
gravitational field is coupled to a scalar field by a parity-violating term,
which gives rise to characteristic signatures. Here we investigate how
Chern-Simons gravity would affect the quasi-circular inspiralling of a small,
stellar-mass object into a large non-rotating supermassive black hole, and the
accompanying emission of gravitational and scalar waves. We find the relevant
equations describing the perturbation induced by the small object, and we solve
them through the use of Green's function techniques. Our results show that for
a wide range of coupling parameters, the Chern-Simons coupling gives rise to an
increase in total energy flux, which translates into a fewer number of
gravitational-wave cycles over a certain bandwidth. For space-based
gravitational-wave detectors such as LISA, this effect can be used to constrain
the coupling parameter effectively.Comment: RevTex4, 18 pages, 7 figures, 1 tabl
Late-Time Tails of Wave Propagation in Higher Dimensional Spacetimes
We study the late-time tails appearing in the propagation of massless fields
(scalar, electromagnetic and gravitational) in the vicinities of a
D-dimensional Schwarzschild black hole. We find that at late times the fields
always exhibit a power-law falloff, but the power-law is highly sensitive to
the dimensionality of the spacetime. Accordingly, for odd D>3 we find that the
field behaves as t^[-(2l+D-2)] at late times, where l is the angular index
determining the angular dependence of the field. This behavior is entirely due
to D being odd, it does not depend on the presence of a black hole in the
spacetime. Indeed this tails is already present in the flat space Green's
function. On the other hand, for even D>4 the field decays as t^[-(2l+3D-8)],
and this time there is no contribution from the flat background. This power-law
is entirely due to the presence of the black hole. The D=4 case is special and
exhibits, as is well known, the t^[-(2l+3)] behavior. In the extra dimensional
scenario for our Universe, our results are strictly correct if the extra
dimensions are infinite, but also give a good description of the late time
behaviour of any field if the large extra dimensions are large enough.Comment: 6 pages, 3 figures, RevTeX4. Version to appear in Rapid
Communications of Physical Review
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