30,653 research outputs found
Two-particle scattering theory for anyons
We consider potential scattering theory of a nonrelativistic quantum
mechanical 2-particle system in R^2 with anyon statistics. Sufficient
conditions are given which guarantee the existence of wave operators and the
unitarity of the S-matrix. As examples the rotationally invariant potential
well and the delta-function potential are discussed in detail. In case of a
general rotationally invariant potential the angular momentum decomposition
leads to a theory of Jost functions. The anyon statistics parameter gives rise
to an interpolation for angular momenta analogous to the Regge trajectories for
complex angular momenta. Levinson's theorem is adapted to the present context.
In particular we find that in case of a zero energy resonance the statistics
parameter can be determined from the scattering phase.Comment: 42 pages of RevTex and 5 figures (included
Topological Charge and the Spectrum of the Fermion Matrix in Lattice-QED_2
We investigate the interplay between topological charge and the spectrum of
the fermion matrix in lattice-QED_2 using analytic methods and Monte Carlo
simulations with dynamical fermions. A new theorem on the spectral
decomposition of the fermion matrix establishes that its real eigenvalues (and
corresponding eigenvectors) play a role similar to the zero eigenvalues (zero
modes) of the Dirac operator in continuous background fields. Using numerical
techniques we concentrate on studying the real part of the spectrum. These
results provide new insights into the behaviour of physical quantities as a
function of the topological charge. In particular we discuss fermion
determinant, effective action and pseudoscalar densities.Comment: 33 pages, 10 eps-figures; reference adde
Symmetries of hadrons after unbreaking the chiral symmetry
We study hadron correlators upon artificial restoration of the spontaneously
broken chiral symmetry. In a dynamical lattice simulation we remove the lowest
lying eigenmodes of the Dirac operator from the valence quark propagators and
study evolution of the hadron masses obtained. All mesons and baryons in our
study, except for a pion, survive unbreaking the chiral symmetry and their
exponential decay signals become essentially better. From the analysis of the
observed spectroscopic patterns we conclude that confinement still persists
while the chiral symmetry is restored. All hadrons fall into different chiral
multiplets. The broken U(1)_A symmetry does not get restored upon unbreaking
the chiral symmetry. We also observe signals of some higher symmetry that
includes chiral symmetry as a subgroup. Finally, from comparison of the \Delta
- N splitting before and after unbreaking of the chiral symmetry we conclude
that both the color-magnetic and the flavor-spin quark-quark interactions are
of equal importance.Comment: 12 pages, 14 figures; final versio
Coherent-feedback quantum control with a dynamic compensator
I present an experimental realization of a coherent-feedback control system
that was recently proposed for testing basic principles of linear quantum
stochastic control theory [M. R. James, H. I. Nurdin and I. R. Petersen, to
appear in IEEE Transactions on Automatic Control (2008),
arXiv:quant-ph/0703150v2]. For a dynamical plant consisting of an optical
ring-resonator, I demonstrate ~ 7 dB broadband disturbance rejection of
injected laser signals via all-optical feedback with a tailored dynamic
compensator. Comparison of the results with a transfer function model pinpoints
critical parameters that determine the coherent-feedback control system's
performance.Comment: 4 pages, 4 EPS figure
Predicting positive parity mesons from lattice QCD
We determine the spectrum of 1P states using lattice QCD. For the
and mesons, the results are in good agreement
with the experimental values. Two further mesons are expected in the quantum
channels and near the and thresholds. A
combination of quark-antiquark and meson-Kaon interpolating fields
are used to determine the mass of two QCD bound states below the
threshold, with the assumption that mixing with and
isospin-violating decays to are negligible. We predict a
bound state with mass GeV. With
further assumptions motivated theoretically by the heavy quark limit, a bound
state with GeV is predicted in the
channel. The results from our first principles calculation are compared to
previous model-based estimates.Comment: 5 pages, 2 figures; Final versio
The Chandra Detection of Galactic Center X-ray Features G359.89-0.08 and G359.54+0.18
We report on the detection of two elongated X-ray features G359.89-0.08 and
G359.54+0.18 in the Galactic center (GC) region using the Chandra X-ray
Observatory. G359.89-0.08 is an elongated X-ray feature located 2\arcmin
in projection south of the center of the Galaxy, SgrA. This X-ray feature
source is partially coincident with a slightly curved (``wisp''-like)
non-thermal radio source. The X-ray spectrum of G359.89-0.08 can be best
characterized as non-thermal, with a photon index of 2. The morphological and
spectral characteristics of the X-ray and radio emission associated with
G359.89-0.08 are best interpreted as the synchrotron emission from a
ram-pressure confined pulsar wind nebula. G359.54+0.18 is one of the most
prominent radio non-thermal filaments (NTFs) in the GC region, located
30\arcmin in projection from SgrA. A narrow (10\arcsec)
filament of X-ray emission appears to arise from one of the two strands that
comprise the radio NTF. Although the photon statistics are poor for this
source, the X-ray emission is also likely to be non-thermal in nature. Several
models for the production of X-ray emission in G359.54+0.18 are discussed.Comment: 19 pages with 6 figures included, accepted by A
The Medicago genome provides insight into the evolution of rhizobial symbioses
Legumes (Fabaceae or Leguminosae) are unique among cultivated plants for their ability to carry out endosymbiotic nitrogen fixation with rhizobial bacteria, a process that takes place in a specialized structure known as the nodule. Legumes belong to one of the two main groups of eurosids, the Fabidae, which includes most species capable of endosymbiotic nitrogen fixation1. Legumes comprise several evolutionary lineages derived from a common ancestor 60 million years ago (Myr ago). Papilionoids are the largest clade, dating nearly to the origin of legumes and containing most cultivated species2. Medicago truncatula is a long-established model for the study of legume biology. Here we describe the draft sequence of the M. truncatula euchromatin based on a recently completed BAC assembly supplemented with Illumina shotgun sequence, together capturing ~94% of all M. truncatula genes. A whole-genome duplication (WGD) approximately 58 Myr ago had a major role in shaping the M. truncatula genome and thereby contributed to the evolution of endosymbiotic nitrogen fixation. Subsequent to the WGD, the M. truncatula genome experienced higher levels of rearrangement than two other sequenced legumes, Glycine max and Lotus japonicus. M. truncatula is a close relative of alfalfa (Medicago sativa), a widely cultivated crop with limited genomics tools and complex autotetraploid genetics. As such, the M. truncatula genome sequence provides significant opportunities to expand alfalfa’s genomic toolbo
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