1,398 research outputs found
Circularly Polarized Resonant Rayleigh Scattering and Skyrmions in the = 1 Quantum Hall Ferromagnet
We use the circularly polarized resonant Rayleigh scattering (RRS) to study
the quantum Hall ferromagnet at = 1. At this filling factor we observe a
right handed copolarized RRS which probes the Skyrmion spin texture of the
electrons in the photoexcited grounds state. The resonant scattering is not
present in the left handed copolarization, and this can be related to the
correlation between Skymionic effects, screening and spin wave excitations.
These results evidence that RRS is a valid method for the study of the spin
texture of the quantum Hall states
Deep inelastic scattering off a N=4 SYM plasma at strong coupling
By using the AdS/CFT correspondence we study the deep inelastic scattering of
an R-current off a N=4 supersymmetric Yang-Mills (SYM) plasma at finite
temperature and strong coupling. Within the supergravity approximation valid
when the number of colors is large, we compute the structure functions by
solving Maxwell equations in the space-time geometry of the AdS_5 black
three-brane. We find a rather sharp transition between a low energy regime
where the scattering is weak and quasi-elastic, and a high-energy regime where
the current is completely absorbed. The critical energy for this transition
determines the plasma saturation momentum in terms of its temperature T and the
Bjorken x variable: Q_s=T/x. These results suggest a partonic picture for the
plasma where all the partons have transverse momenta below the saturation
momentum and occupation numbers of order one.Comment: Version accepted for publication in JHEP: more references added; some
technical points were displaced from Sect. 4 to the new Appendix
Form-function relationship in the amplitude and frequency modulations of infant - directed speech: A predictive processing perspective
Infants prefer infant-directed speech (IDS) over adult-directed speech (ADS). IDS is thought to serve specific functions compared to ADS:
- Attracting infant attention to the speech signal
- Conveying clear opportunities for easier word segmentation.
Two independent domains of complexity that are embedded in the speech stream:
- Amplitude complexity: Lower amplitude complexity associates with greater ease in identifying word boundaries
​
- ​Frequency complexity: Higher fre q uency complexity associates with more attention eliciting speech attention by inducing uncertaint
Striped instability of a holographic Fermi-like liquid
We consider a holographic description of a system of strongly-coupled
fermions in 2+1 dimensions based on a D7-brane probe in the background of
D3-branes. The black hole embedding represents a Fermi-like liquid. We study
the excitations of the Fermi liquid system. Above a critical density which
depends on the temperature, the system becomes unstable towards an
inhomogeneous modulated phase which is similar to a charge density and spin
wave state. The essence of this instability can be effectively described by a
Maxwell-axion theory with a background electric field. We also consider the
fate of zero sound at non-zero temperature.Comment: 16 pages, 9 figures; v2: added discussion and one figure. Typos
correcte
Black holes and black branes in Lifshitz spacetimes
We construct analytic solutions describing black holes and black branes in
asymptotically Lifshitz spacetimes with arbitrary dynamical exponent z and for
arbitrary number of dimensions. The model considered consists of Einstein
gravity with negative cosmological constant, a scalar, and N U(1) gauge fields
with dilatonic-like couplings. We study the phase diagrams and thermodynamic
instabilities of the solution, and find qualitative differences between the
cases with 12.Comment: 27 pages, 10 figures; v2 references added, minor comments adde
Gravitational quasinormal modes of AdS black branes in d spacetime dimensions
The AdS/CFT duality has established a mapping between quantities in the bulk
AdS black-hole physics and observables in a boundary finite-temperature field
theory. Such a relationship appears to be valid for an arbitrary number of
spacetime dimensions, extrapolating the original formulations of Maldacena's
correspondence. In the same sense properties like the hydrodynamic behavior of
AdS black-hole fluctuations have been proved to be universal. We investigate in
this work the complete quasinormal spectra of gravitational perturbations of
-dimensional plane-symmetric AdS black holes (black branes). Holographically
the frequencies of the quasinormal modes correspond to the poles of two-point
correlation functions of the field-theory stress-energy tensor. The important
issue of the correct boundary condition to be imposed on the gauge-invariant
perturbation fields at the AdS boundary is studied and elucidated in a fully
-dimensional context. We obtain the dispersion relations of the first few
modes in the low-, intermediate- and high-wavenumber regimes. The sound-wave
(shear-mode) behavior of scalar (vector)-type low-frequency quasinormal mode is
analytically and numerically confirmed. These results are found employing both
a power series method and a direct numerical integration scheme.Comment: added references, typos corrected, minor changes, final version for
JHE
Quasinormal modes of massive charged flavor branes
We present an analysis and classification of vector and scalar fluctuations
in a D3/D7 brane setup at finite termperature and baryon density. The system is
dual to an N=2 supersymmetric Yang-Mills theory with SU(N_c) gauge group and
N_f hypermultiplets in the fundamental representation in the quenched
approximation. We improve significantly over previous results on the
quasinormal mode spectrum of D7 branes and stress their novel physical
interpretation. Amongst our findings is a new purely imaginary scalar mode that
becomes tachyonic at sufficiently low temperature and baryon density. We
establish the existence of a critical density above which the scalar mode stays
in the stable regime for all temperatures. In the vector sector we study the
crossover from the hydrodynamic to the quasiparticle regime and find that it
moves to shorter wavelengths for lower temperatures. At zero baryon density the
quasinormal modes move toward distinct discrete attractor frequencies that
depend on the momentum as we increase the temperature. At finite baryon
density, however, the trajectories show a turning behavior such that for low
temperature the quasinormal mode spectrum approaches the spectrum of the
supersymmetric zero temperature normal modes. We interpret this as resolution
of the singular quasinormal mode spectrum that appears at the limiting D7 brane
embedding at vanishing baryon density.Comment: 56 pages, 40 figure
Black-hole quasinormal modes and scalar glueballs in a finite-temperature AdS/QCD model
We use the holographic AdS/QCD soft-wall model to investigate the spectrum of
scalar glueballs in a finite temperature plasma. In this model, glueballs are
described by a massless scalar field in an AdS_5 black hole with a dilaton
soft-wall background. Using AdS/CFT prescriptions, we compute the boundary
retarded Green's function. The corresponding thermal spectral function shows
quasiparticle peaks at low temperatures. We also compute the quasinormal modes
of the scalar field in the soft-wall black hole geometry. The temperature and
momentum dependences of these modes are analyzed. The positions and widths of
the peaks of the spectral function are related to the frequencies of the
quasinormal modes. Our numerical results are found employing the power series
method and the computation of Breit-Wigner resonances.Comment: Revision: Results unchanged. More discussions on the model and on the
results. References added. 28 pages, 7 figures, 5 table
Implementación de un algoritmo de morfogénesis para el diseño de disipadores de calor
Este artÃculo presenta el resultado de un trabajo de investigación que pretende realizar el diseño de un disipador de calor, optimizado para las proporciones del empaquetado para transistores TO-220, por medio de un algoritmo de morfogénesis realizado en Matlab. Este algoritmo toma como base la lógica de los sistemas Lindenmayer con el fin de crear formas en dos dimensiones para ser optimizadas a través de un algoritmo genético. Posteriormente se evidencian los diversos comportamientos de dichas formas en cuanto a la disipación de calor, por medio de simulaciones térmicas en el toobox PDEtool de Matlab
The holographic superconductors in higher-dimensional AdS soliton
We explore the behaviors of the holographic superconductors at zero
temperature for a charged scalar field coupled to a Maxwell field in
higher-dimensional AdS soliton spacetime via analytical way. In the probe
limit, we obtain the critical chemical potentials increase linearly as a total
dimension grows up. We find that the critical exponent for condensation
operator is obtained as 1/2 independently of , and the charge density is
linearly related to the chemical potential near the critical point.
Furthermore, we consider a slightly generalized setup the
Einstein-Power-Maxwell field theory, and find that the critical exponent for
condensation operator is given as in terms of a power parameter
of the Power-Maxwell field, and the charge density is proportional to the
chemical potential to the power of .Comment: LaTeX, 16 pages, 5 figures, typos corrected, one reference added,
version to appear in European Physical Journal
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