386 research outputs found
Energy absorption in time-dependent unitary random matrix ensembles: dynamic vs Anderson localization
We consider energy absorption in an externally driven complex system of
noninteracting fermions with the chaotic underlying dynamics described by the
unitary random matrices. In the absence of quantum interference the energy
absorption rate W(t) can be calculated with the help of the linear-response
Kubo formula. We calculate the leading two-loop interference correction to the
semiclassical absorption rate for an arbitrary time dependence of the external
perturbation. Based on the results for periodic perturbations, we make a
conjecture that the dynamics of the periodically-driven random matrices can be
mapped onto the one-dimensional Anderson model. We predict that in the regime
of strong dynamic localization W(t) ln(t)/t^2 rather than decays exponentially.Comment: 6 pages, 1 figur
Interference induced metallic-like behavior of a two-dimensional hole gas in asymmetric GaAs/InGaAs/GaAs quantum well
The temperature and magnetic field dependences of the conductivity of the
heterostructures with asymmetric InGaAs quantum well are studied.
It is shown that the metallic-like temperature dependence of the conductivity
observed in the structures investigated is quantitatively understandable within
the whole temperature range, K. It is caused by the interference
quantum correction at fast spin relaxation for 0.4 K K. At higher
temperatures, 1.5 K K, it is due to the interaction quantum correction.
Finally, at K, the metallic-like behavior is determined by the phonon
scattering.Comment: 4 pages, 4 figure
Level statistics inside the core of a superconductive vortex
Microscopic theory of the type of Efetov's supermatrix sigma-model is
constructed for the low-lying electron states in a mixed superconductive-normal
system with disorder. The developed technique is used for the study of the
localized states in the core of a vortex in a moderately clean superconductor
(1/\Delta << \tau << 1/\omega_0 = E_F/\Delta^2). At sufficiently low energies E
<< \omega_{Th}, the energy level statistics is described by the
"zero-dimensional" limit of this supermatrix theory, with the effective
"Thouless energy" \omega_{Th} \sim (\omega_0/\tau)^{1/2}. Within this energy
range the result for the density of states is equivalent to that obtained
within Altland-Zirnbauer random matrix model of class C. Nonzero modes of the
sigma-model increase the mean interlevel distance \omega_0 by the relative
amount of the order of [2\ln(1/\omega_0\tau)]^{-1}.Comment: 5 pages, RevTeX. One error is corrected, also two references are
added. Submitted to JETP Letter
Unfolded Scalar Supermultiplet
Unfolded equations of motion for N = 1, D = 4 scalar supermultiplet are
presented. We show how the superspace formulation emerges from the unfolded
formulation. To analyze supersymmetric unfolded equations we extend the
\sigma_-cohomology technics to the case with several operators \sigma_. The
role of higher \sigma_-cohomology in the derivation of constraints is
emphasized and illustrated by the example of scalar supermultiplet.Comment: 27 pages, no figures; minor corrections: clarifications added, typos
correcte
Maxwell-like Lagrangians for higher spins
We show how implementing invariance under divergence-free gauge
transformations leads to a remarkably simple Lagrangian description of massless
bosons of any spin. Our construction covers both flat and (A)dS backgrounds and
extends to tensors of arbitrary mixed-symmetry type. Irreducible and traceless
fields produce single-particle actions, while whenever trace constraints can be
dispensed with the resulting Lagrangians display the same reducible,
multi-particle spectra as those emerging from the tensionless limit of free
open-string field theory. For all explored options the corresponding kinetic
operators take essentially the same form as in the spin-one, Maxwell case.Comment: 77 pages, revised version. Erroneous interpretation and proof of the
gauge-fixing procedure for mixed-symmetry fields corrected. As a consequence,
the mixed-symmetry, one-particle Lagrangians are to be complemented with
conditions on the divergences of the fields; all other conclusions unchanged.
Additional minor changes including references added. To appear in JHE
Gauge fields in (A)dS within the unfolded approach: algebraic aspects
It has recently been shown that generalized connections of the (A)dS space
symmetry algebra provide an effective geometric and algebraic framework for all
types of gauge fields in (A)dS, both for massless and partially-massless. The
equations of motion are equipped with a nilpotent operator called
whose cohomology groups correspond to the dynamically relevant quantities like
differential gauge parameters, dynamical fields, gauge invariant field
equations, Bianchi identities etc. In the paper the -cohomology is
computed for all gauge theories of this type and the field-theoretical
interpretation is discussed. In the simplest cases the -cohomology is
equivalent to the ordinary Lie algebra cohomology.Comment: 59 pages, replaced with revised verio
STUDY AND ANALYSIS OF TERMINOLOGY IN THE FIELD OF NANOTECHNOLOGIES IN MEDICINE IN THE ENGLISH AND RUSSIAN LANGUAGES
The given work describes the results of stratificational analysis of special vocabulary in the sphere of nanotechnologies in medicine in the Russian and English language. The analysis showed that the most commonly used terms are those of describing concrete objects
First order parent formulation for generic gauge field theories
We show how a generic gauge field theory described by a BRST differential can
systematically be reformulated as a first order parent system whose spacetime
part is determined by the de Rham differential. In the spirit of Vasiliev's
unfolded approach, this is done by extending the original space of fields so as
to include their derivatives as new independent fields together with associated
form fields. Through the inclusion of the antifield dependent part of the BRST
differential, the parent formulation can be used both for on and off-shell
formulations. For diffeomorphism invariant models, the parent formulation can
be reformulated as an AKSZ-type sigma model. Several examples, such as the
relativistic particle, parametrized theories, Yang-Mills theory, general
relativity and the two dimensional sigma model are worked out in details.Comment: 36 pages, additional sections and minor correction
Anomalous flux-flow dynamics in layered type-II superconductors at low temperatures
Low-temperature dissipation due to vortex motion in strongly anisotropic
type-II superconductors with a moderate disorder () is shown to be determined by the Zener-type transitions between
the localized electronic states in the vortex core. Statistics of these levels
is described by the random matrix ensemble of the class C defined recently by
Atland and Zirnbauer [cond-mat/9602137], so the vortex motion leads naturally
to the new example of a parametric statistics of energy levels. The flux-flow
conductivity is a bit lower than the quasiclassical one and {\it
grows} slowly with the increase of the electric field.Comment: 4 pages, Revte
Local correlations of different eigenfunctions in a disordered wire
We calculate the correlator of the local density of states
in quasi-one-dimensional disordered wires
in a magnetic field, assuming that |r_1-r_2| is much smaller than the
localization length. This amounts to finding the zero mode of the
transfer-matrix Hamiltonian for the supersymmetric sigma-model, which is done
exactly by the mapping to the three-dimensional Coulomb problem. Both the
regimes of level repulsion and level attraction are obtained, depending on
|r_1-r_2|. We demonstrate that the correlations of different eigenfunctions in
the quasi-one-dimensional and strictly one-dimensional cases are dissimilar.Comment: 5 pages, 2 figures. v2: an error in treating the spatial dependence
of correlations is correcte
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