128 research outputs found
Random Aharonov-Bohm vortices and some funny families of integrals
A review of the random magnetic impurity model, introduced in the context of
the integer Quantum Hall effect, is presented. It models an electron moving in
a plane and coupled to random Aharonov-Bohm vortices carrying a fraction of the
quantum of flux. Recent results on its perturbative expansion are given. In
particular, some funny families of integrals show up to be related to the
Riemann and .Comment: 10 page
Hall Conductivity for Two Dimensional Magnetic Systems
A Kubo inspired formalism is proposed to compute the longitudinal and
transverse dynamical conductivities of an electron in a plane (or a gas of
electrons at zero temperature) coupled to the potential vector of an external
local magnetic field, with the additional coupling of the spin degree of
freedom of the electron to the local magnetic field (Pauli Hamiltonian). As an
example, the homogeneous magnetic field Hall conductivity is rederived. The
case of the vortex at the origin is worked out in detail. This system happens
to display a transverse Hall conductivity ( breaking effect) which is
subleading in volume compared to the homogeneous field case, but diverging at
small frequency like . A perturbative analysis is proposed for the
conductivity in the random magnetic impurity problem (Poissonian vortices in
the plane). At first order in perturbation theory, the Hall conductivity
displays oscillations close to the classical straight line conductivity of the
mean magnetic field.Comment: 28 pages, latex, 2 figure
On a different BRST constructions for a given Lie algebra
The method of the BRST quantization is considered for the system of
constraints, which form a Lie algebra. When some of the Cartan generators do
not imply any conditions on the physical states, the system contains the first
and the second class constraints. After the introduction auxiliary bosonic
degrees of freedom for these cases, the corresponding BRST charges with the
nontrivial structure of nonlinear terms in ghosts are constructed.Comment: 10 Pages, LaTe
Persistent Current of Free Electrons in the Plane
Predictions of Akkermans et al. are essentially changed when the Krein
spectral displacement operator is regularized by means of zeta function.
Instead of piecewise constant persistent current of free electrons on the plane
one has a current which varies linearly with the flux and is antisymmetric with
regard to all time preserving values of including . Different
self-adjoint extensions of the problem and role of the resonance are discussed.Comment: (Comment on "Relation between Persistent Currents and the Scattering
Matrix", Phys. Rev. Lett. {\bf 66}, 76 (1991)) plain latex, 4pp., IPNO/TH
94-2
Area distribution of two-dimensional random walks on a square lattice
The algebraic area probability distribution of closed planar random walks of
length N on a square lattice is considered. The generating function for the
distribution satisfies a recurrence relation in which the combinatorics is
encoded. A particular case generalizes the q-binomial theorem to the case of
three addends. The distribution fits the L\'evy probability distribution for
Brownian curves with its first-order 1/N correction quite well, even for N
rather small.Comment: 8 pages, LaTeX 2e. Reformulated in terms of q-commutator
Direct sequence spread spectrum sequences
DS-CDMA (for Direct-Sequence Code-Division Multiple-Access, in english, or AMRC, for Accès Multiple à Répartition par les
Codes, in french) receivers are significantly performance degraded by the non-orthogonality of the classicaly used spreading
sequences, mainly because of the odd correlation functions . The "Tabu Search" algorithm enables sequence generation optimising
various criteria . The obtained performance are better than those of the Litterature . Moreover, the proposed method enables the
optimisation of sequence sets of any desired length and cardinal, what is not the case for the previous mathematically constructed
sequences .Les récepteurs DS-CDMA (pour Direct-Sequence Code-Division Multiple-Access, en anglais, ou AMRC, pour Accès Multiple à Répartition par les Codes, en français) voient leur performance être dégradée de manière significative par la non-orthogonalité des séquences d'étalement classiquement utilisées et principalement à cause des fonctions de corrélation impaires. L'algorithme dit de « Recherche Taboue » (ou Tabu Search, en anglais) permet la génération de séquences optimisant différents critères. Les performances obtenues sont meilleures que celles des séquences de la littérature. De plus, la démarche exposée permet d'optimiser des jeux de séquences de longueur et de cardinal quelconques, ce qui n'est pas le cas des séquences construites de manière mathématique
Finite-size anyons and perturbation theory
We address the problem of finite-size anyons, i.e., composites of charges and
finite radius magnetic flux tubes. Making perturbative calculations in this
problem meets certain difficulties reminiscent of those in the problem of
pointlike anyons. We show how to circumvent these difficulties for anyons of
arbitrary spin. The case of spin 1/2 is special because it allows for a direct
application of perturbation theory, while for any other spin, a redefinition of
the wave function is necessary. We apply the perturbative algorithm to the
N-body problem, derive the first-order equation of state and discuss some
examples.Comment: 18 pages (RevTex) + 4 PS figures (all included); a new section on
equation of state adde
Universal Hidden Supersymmetry in Classical Mechanics and its Local Extension
We review here a path-integral approach to classical mechanics and explore
the geometrical meaning of this construction. In particular we bring to light a
universal hidden BRS invariance and its geometrical relevance for the Cartan
calculus on symplectic manifolds. Together with this BRS invariance we also
show the presence of a universal hidden genuine non-relativistic supersymmetry.
In an attempt to understand its geometry we make this susy local following the
analogous construction done for the supersymmetric quantum mechanics of Witten.Comment: 6 pages, latex, Volkov Memorial Proceeding
Classical limit for the scattering of Dirac particles in a magnetic field
We present a relativistic quantum calculation at first order in perturbation
theory of the differential cross section for a Dirac particle scattered by a
solenoidal magnetic field. The resulting cross section is symmetric in the
scattering angle as those obtained by Aharonov and Bohm (AB) in the string
limit and by Landau and Lifshitz (LL) for the non relativistic case. We show
that taking pr_0\|sin(\theta/2)|/\hbar<<1 in our expression of the differential
cross section it reduces to the one reported by AB, and if additionally we
assume \theta << 1 our result becomes the one obtained by LL. However, these
limits are explicitly singular in \hbar as opposed to our initial result. We
analyze the singular behavior in \hbar and show that the perturbative Planck's
limit (\hbar -> 0) is consistent, contrarily to those of the AB and LL
expressions. We also discuss the scattering in a uniform and constant magnetic
field, which resembles some features of QCD
Conductance and Shot Noise for Particles with Exclusion Statistics
The first quantized Landauer approach to conductance and noise is generalized
to particles obeying exclusion statistics. We derive an explicit formula for
the crossover between the shot and thermal noise limits and argue that such a
crossover can be used to determine experimentally whether charge carriers in
FQHE devices obey exclusion statistics.Comment: 4 pages, revtex, 1 eps figure include
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