299 research outputs found
Hall Conductance of a Two-Dimensional Electron Gas in Periodic Lattice with Triangular Antidots
The topic of this contribution is the investigation of quantum states and
quantum Hall effect in electron gas subjected to a periodic potential of the
lateral lattice. The potential is formed by triangular quantum antidos located
on the sites of the square lattice. In a such system the inversion center and
the four-fold rotation symmetry are absent. The topological invariants which
characterize different magnetic subbands and their Hall conductances are
calculated. It is shown that the details of the antidot geometry are crucial
for the Hall conductance quantization rule. The critical values of lattice
parameters defining the shape of triangular antidots at which the Hall
conductance is changed drastically are determined. We demonstrate that the
quantum states and Hall conductance quantization law for the triangular antidot
lattice differ from the case of the square lattice with cylindrical antidots.
As an example, the Hall conductances of magnetic subbands for different antidot
geometries are calculated for the case when the number of magnetic flux quanta
per unit cell is equal to three.Comment: 6 pages, 5 figure
Euclidean Correlation Functions in a Holographic Model of QCD
We compute euclidean coordinate space correlation functions in a holographic
model of QCD. We concentrate, in particular, on channels that are related to
the U(1)_A problem, the flavor-singlet axialvector, pseudoscalar meson, and
pseudoscalar glueball (topological charge) correlator. We find that even a very
simple holographic model defined on a slice of AdS_5 provides a qualitatively
correct description of QCD correlation functions. We study the role of anomaly
terms, and show that both euclidean positivity and low energy theorems based on
the axial anomaly relation are correctly implemented. We compare the results
with expectations from an instanton model of the QCD vacuum.Comment: 16 pages, 5 figures, minor changes (references added), to appear in
Phys Rev
2d Gauge Theories and Generalized Geometry
We show that in the context of two-dimensional sigma models minimal coupling
of an ordinary rigid symmetry Lie algebra leads naturally to the
appearance of the "generalized tangent bundle" by means of composite fields. Gauge transformations of the composite
fields follow the Courant bracket, closing upon the choice of a Dirac structure
(or, more generally, the choide of a "small
Dirac-Rinehart sheaf" ), in which the fields as well as the symmetry
parameters are to take values. In these new variables, the gauge theory takes
the form of a (non-topological) Dirac sigma model, which is applicable in a
more general context and proves to be universal in two space-time dimensions: A
gauging of of a standard sigma model with Wess-Zumino term
exists, \emph{iff} there is a prolongation of the rigid symmetry to a Lie
algebroid morphism from the action Lie algebroid
into (or the algebraic analogue of the morphism in the case of
). The gauged sigma model results from a pullback by this morphism
from the Dirac sigma model, which proves to be universal in two-spacetime
dimensions in this sense.Comment: 22 pages, 2 figures; To appear in Journal of High Energy Physic
Preliminary Limits on the WIMP-Nucleon Cross Section from the Cryogenic Dark Matter Search (CDMS)
We are conducting an experiment to search for WIMPs, or weakly-interacting
massive particles, in the galactic halo using terrestrial detectors. This
generic class of hypothetical particles, whose properties are similar to those
predicted by extensions of the standard model of particle physics, could
comprise the cold component of non-baryonic dark matter. We describe our
experiment, which is based on cooled germanium and silicon detectors in a
shielded low-background cryostat. The detectors achieve a high degree of
background rejection through the simultaneous measurement of the energy in
phonons and ionization. Using exposures on the order of one kilogram-day from
initial runs of our experiment, we have achieved (preliminary) upper limits on
the WIMP-nucleon cross section that are comparable to much longer runs of other
experiments.Comment: 5 LaTex pages, 5 eps figs, epsf.sty, espcrc2dsa2.sty. Proceedings of
TAUP97, Gran Sasso, Italy, 7-11 Sep 1997, Nucl. Phys. Suppl., A. Bottino, A.
di Credico and P. Monacelli (eds.). See also http://cfpa.berkeley.ed
5-arylaminouracil derivatives as potential dual-action agents
Several 5-aminouracil derivatives that have previously been shown to inhibit Mycobacterium tuberculosis growth at concentrations of 5-40 ÎŒg/mL are demonstrated to act also as noncompetitive non-nucleoside inhibitors of HIV-1 reverse transcriptase without causing toxicity in vitro (McyrillicT-4 cells) and ex vivo (human tonsillar tissue)
Addition of N-nucleophiles to gold(III)-bound isocyanides leading to short-lived gold(III) acyclic diaminocarbene complexes
Addition of hydrazone to gold(iii)âisocyanides led to the generation of rare short-lived gold(iii) acyclic diaminocarbene complexes.</p
Gross-Neveu Models, Nonlinear Dirac Equations, Surfaces and Strings
Recent studies of the thermodynamic phase diagrams of the Gross-Neveu model
(GN2), and its chiral cousin, the NJL2 model, have shown that there are phases
with inhomogeneous crystalline condensates. These (static) condensates can be
found analytically because the relevant Hartree-Fock and gap equations can be
reduced to the nonlinear Schr\"odinger equation, whose deformations are
governed by the mKdV and AKNS integrable hierarchies, respectively. Recently,
Thies et al have shown that time-dependent Hartree-Fock solutions describing
baryon scattering in the massless GN2 model satisfy the Sinh-Gordon equation,
and can be mapped directly to classical string solutions in AdS3. Here we
propose a geometric perspective for this result, based on the generalized
Weierstrass spinor representation for the embedding of 2d surfaces into 3d
spaces, which explains why these well-known integrable systems underlie these
various Gross-Neveu gap equations, and why there should be a connection to
classical string theory solutions. This geometric viewpoint may be useful for
higher dimensional models, where the relevant integrable hierarchies include
the Davey-Stewartson and Novikov-Veselov systems.Comment: 27 pages, 1 figur
Random walk with barriers: Diffusion restricted by permeable membranes
Restrictions to molecular motion by barriers (membranes) are ubiquitous in
biological tissues, porous media and composite materials. A major challenge is
to characterize the microstructure of a material or an organism
nondestructively using a bulk transport measurement. Here we demonstrate how
the long-range structural correlations introduced by permeable membranes give
rise to distinct features of transport. We consider Brownian motion restricted
by randomly placed and oriented permeable membranes and focus on the
disorder-averaged diffusion propagator using a scattering approach. The
renormalization group solution reveals a scaling behavior of the diffusion
coefficient for large times, with a characteristically slow inverse square root
time dependence. The predicted time dependence of the diffusion coefficient
agrees well with Monte Carlo simulations in two dimensions. Our results can be
used to identify permeable membranes as restrictions to transport in disordered
materials and in biological tissues, and to quantify their permeability and
surface area.Comment: 8 pages, 3 figures; origin of dispersion clarified, refs adde
The , , and mesons in a double pole QCD Sum Rule
We use the method of double pole QCD sum rule which is basically a fit with
two exponentials of the correlation function, where we can extract the masses
and decay constants of mesons as a function of the Borel mass. We apply this
method to study the mesons: , , and
. We also present predictions for the toponiuns masses
of m(1S)=357 GeV and m(2S)=374 GeV.Comment: 14 pages, 11 figures in Braz J Phys (2016
Algorithmic Integrability Tests for Nonlinear Differential and Lattice Equations
Three symbolic algorithms for testing the integrability of polynomial systems
of partial differential and differential-difference equations are presented.
The first algorithm is the well-known Painlev\'e test, which is applicable to
polynomial systems of ordinary and partial differential equations. The second
and third algorithms allow one to explicitly compute polynomial conserved
densities and higher-order symmetries of nonlinear evolution and lattice
equations.
The first algorithm is implemented in the symbolic syntax of both Macsyma and
Mathematica. The second and third algorithms are available in Mathematica. The
codes can be used for computer-aided integrability testing of nonlinear
differential and lattice equations as they occur in various branches of the
sciences and engineering. Applied to systems with parameters, the codes can
determine the conditions on the parameters so that the systems pass the
Painlev\'e test, or admit a sequence of conserved densities or higher-order
symmetries.Comment: Submitted to: Computer Physics Communications, Latex, uses the style
files elsart.sty and elsart12.st
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