13,813 research outputs found
Quasinormal Modes of Charged Scalars around Dilaton Black Holes in 2+1 Dimensions: Exact Frequencies
We have studied the charged scalar perturbation around a dilaton black hole
in 2 +1 dimensions. The wave equations of a massless charged scalar field is
shown to be exactly solvable in terms of hypergeometric functions. The
quasinormal frequencies are computed exactly. The relation between the
quasinormal frequencies and the charge of the black hole, charge of the scalar
and the temperature of the black hole are analyzed. The asymptotic form of the
real part of the quasinormal frequencies are evaluated exactly.Comment: 20 pages and 7 figures, some references are added and some removed.
There are some changes to the text. arXiv admin note: text overlap with
arXiv:hep-th/040716
Soft SUSY Breaking Terms for Chiral Matter in IIB String Compactifications
This paper develops the computation of soft supersymmetry breaking terms for
chiral D7 matter fields in IIB Calabi-Yau flux compactifications with
stabilised moduli. We determine explicit expressions for soft terms for the
single-modulus KKLT scenario and the multiple-moduli large volume scenario. In
particular we use the chiral matter metrics for Calabi-Yau backgrounds recently
computed in hep-th/0609180. These differ from the better understood metrics for
non-chiral matter and therefore give a different structure of soft terms. The
soft terms take a simple form depending explicitly on the modular weights of
the corresponding matter fields. For the large-volume case we find that in the
simplest D7 brane configuration, scalar masses, gaugino masses and A-terms are
very similar to the dilaton-dominated scenario. Although all soft masses are
suppressed by ln(M_P/m_{3/2}) compared to the gravitino mass, the
anomaly-mediated contributions do not compete, being doubly suppressed and thus
subdominant to the gravity-mediated tree-level terms. Soft terms are
flavour-universal to leading order in an expansion in inverse Kahler moduli.
They also do not introduce extra CP violating phases to the effective action.
We argue that soft term flavour universality should be a property of the
large-volume compactifications, and more generally IIB flux models, in which
flavour is determined by the complex structure moduli while supersymmetry is
broken by the Kahler moduli. For the simplest large-volume case we run the soft
terms to low energies and present some sample spectra and a basic
phenomenological analysis.Comment: 40 pages, 9 figures, JHEP style; v2. sentence rephrase
When does noise increase the quantum capacity?
Superactivation is the property that two channels with zero quantum capacity
can be used together to yield positive capacity. Here we demonstrate that this
effect exists for a wide class of inequivalent channels, none of which can
simulate each other. We also consider the case where one of two zero capacity
channels are applied, but the sender is ignorant of which one is applied. We
find examples where the greater the entropy of mixing of the channels, the
greater the lower bound for the capacity. Finally, we show that the effect of
superactivation is rather generic by providing example of superactivation using
the depolarizing channel.Comment: Corrected minor typo
Geometric phases under the presence of a composite environment
We compute the geometric phase for a spin-1/2 particle under the presence of
a composite environment, composed of an external bath (modeled by an infinite
set of harmonic oscillators) and another spin-1/2 particle. We consider both
cases: an initial entanglement between the spin-1/2 particles and an initial
product state in order to see if the initial entanglement has an enhancement
effect on the geometric phase of one of the spins. We follow the nonunitary
evolution of the reduced density matrix and evaluate the geometric phase for a
single two-level system. We also show that the initial entanglement enhances
the sturdiness of the geometric phase under the presence of an external
composite environment.Comment: 10 pages, 12 figures. Version to appear in Phys. Rev.
Quasinormal Modes of Bardeen Black Hole: Scalar Perturbations
The purpose of this paper is to study quasinormal modes (QNM) of the Bardeen
black hole due to scalar perturbations. We have done a thorough analysis of the
QNM frequencies by varying the charge , mass and the spherical harmonic
index . The unstable null geodesics are used to compute the QNM's in the
eikonal limit. Furthermore, massive scalar field modes are also studied by
varying the mass of the field. Comparisons are done with the QNM frequencies of
the Reissner-Nordstrom black hole.Comment: 25 figures, Published in Physical Review D. Reference numbers
correcte
Electromotive force and internal resistance of an electron pump
We present a scattering theory of the electromotive force and internal
resistance of an electron pump. The characterization of the device performance
in terms of only two parameters requires the assumption of incoherent multiple
scattering within the circuit and complete thermalization among electrons
moving in a given direction. The electromotive force is shown to be of the
order of the driving frequency in natural units. In an open setup, the
electromotive force adds to the voltage difference between reservoirs to drive
the current, both facing a contact resistance which is absent in the case of a
closed circuit of uniform width
Probing Quantized Einstein-Rosen Waves with Massless Scalar Matter
The purpose of this paper is to discuss in detail the use of scalar matter
coupled to linearly polarized Einstein-Rosen waves as a probe to study quantum
gravity in the restricted setting provided by this symmetry reduction of
general relativity. We will obtain the relevant Hamiltonian and quantize it
with the techniques already used for the purely gravitational case. Finally we
will discuss the use of particle-like modes of the quantized fields to
operationally explore some of the features of quantum gravity within this
framework. Specifically we will study two-point functions, the Newton-Wigner
propagator, and radial wave functions for one-particle states.Comment: Accepted for publication in Physical Review
Dispersal and population structure at different spatial scales in the subterranean rodent Ctenomys australis
This study was funded by grants from Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas (CONICET, PIP5838), Agencia de PromociĂłn CientĂfica y TecnolĂłgica de la Argentina (PICTO1-423, BID-1728/OC-AR), and the programme ECOS-Sud France/Argentina (A05B01).Background: The population genetic structure of subterranean rodent species is strongly affected by demographic (e.g. rates of dispersal and social structure) and stochastic factors (e.g. random genetic drift among subpopulations and habitat fragmentation). In particular, gene flow estimates at different spatial scales are essential to understand genetic differentiation among populations of a species living in a highly fragmented landscape. Ctenomys australis (the sand dune tuco-tuco) is a territorial subterranean rodent that inhabits a relatively secure, permanently sealed burrow system, occurring in sand dune habitats on the coastal landscape in the south-east of Buenos Aires province, Argentina. Currently, this habitat is threatened by urban development and forestry and, therefore, the survival of this endemic species is at risk. Here, we assess population genetic structure and patterns of dispersal among individuals of this species at different spatial scales using 8 polymorphic microsatellite loci. Furthermore, we evaluate the relative importance of sex and habitat configuration in modulating the dispersal patterns at these geographical scales. Results: Our results show that dispersal in C. australis is not restricted at regional spatial scales (similar to 4 km). Assignment tests revealed significant population substructure within the study area, providing support for the presence of two subpopulations from three original sampling sites. Finally, male-biased dispersal was found in the Western side of our study area, but in the Eastern side no apparent philopatric pattern was found, suggesting that in a more continuous habitat males might move longer distances than females. Conclusions: Overall, the assignment-based approaches were able to detect population substructure at fine geographical scales. Additionally, the maintenance of a significant genetic structure at regional (similar to 4 km) and small (less than 1 km) spatial scales despite apparently moderate to high levels of gene flow between local sampling sites could not be explained simply by the linear distance among them. On the whole, our results support the hypothesis that males disperse more frequently than females; however they do not provide support for strict philopatry within females.Publisher PDFPeer reviewe
Dephasing in matter-wave interferometry
We review different attempts to show the decoherence process in
double-slit-like experiments both for charged particles (electrons) and neutral
particles with permanent dipole moments. Interference is studied when electrons
or atomic systems are coupled to classical or quantum electromagnetic fields.
The interaction between the particles and time-dependent fields induces a
time-varying Aharonov phase. Averaging over the phase generates a suppression
of fringe visibility in the interference pattern. We show that, for suitable
experimental conditions, the loss of contrast for dipoles can be almost as
large as the corresponding one for coherent electrons and therefore, be
observed. We analyze different trajectories in order to show the dependence of
the decoherence factor with the velocity of the particles.Comment: 9 pages, 1 eps-figure. To appear in J. Phys. A: Math. Ge
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