3,299 research outputs found
Probing the gluon self-interaction in light mesons
We investigate masses and decay constants of light mesons from a coupled
system of Dyson--Schwinger and Bethe--Salpeter equations. We explicitly take
into account dominant non-Abelian contributions to the dressed quark-gluon
vertex stemming from the gluon self-interaction. We construct the corresponding
Bethe-Salpeter kernel that satisfies the axial-vector Ward-Takahashi identity.
Our numerical treatment fully includes all momentum dependencies with all
equations solved completely in the complex plane. This approach goes well
beyond the rainbow-ladder approximation and permits us to investigate the
influence of the gluon self-interaction on the properties of mesons. As a first
result we find indications of a nonperturbative cancellation of the gluon
self-interaction contributions and pion cloud effects in the mass of the
rho-meson.Comment: 4 pages, 5 figures. Matches published version in PR
Beyond the rainbow: effects from pion back-coupling
We investigate hadronic unquenching effects in light quarks and mesons. To
this end we take into account the back-coupling of the pion onto the quark
propagator within the non-perturbative continuum framework of Schwinger-Dyson
equations (SDE) and Bethe-Salpeter equations (BSE). We improve on a previous
approach by explicitly solving both the coupled system of DSEs and BSEs in the
complex plane and the normalisation problem for Bethe-Salpeter kernels
depending on the total momentum of the meson. As a result of our study we find
considerable unquenching effects in the spectrum of light pseudoscalar, vector
and axial-vector mesons.Comment: 9 pages, 5 figures. Minor typos corrected. Version to appear in PR
Realization of an Economical Polymer Optical Fiber Demultiplexer
Polymer Optical Fiber (POF) can be and are being used in various fields of
applications. Two of the main fields are the automotive and the home
entertainment sector. The POF can be applied in several different optical
communication systems as automotive multi-media busses or in-house Ethernet
systems.
The requirements of bandwidth are increasing very fast in these sectors and
therefore solutions that satisfy these demands are of high actuality. One
solution is to use the wavelength division multiplexing (WDM) technique. Here,
several different wavelengths can carry information over one POF fiber. All
wavelengths that are transmitted over the fiber, must be separated at the
receiver to regain and redirect the information channels. These separators are
so-called Demultiplexers.
There are several systems available on the market, which are all afflicted
with certain disadvantages. But all these solutions have one main disadvantage,
they are all too expensive for most of the applications mentioned above. So the
goal of this study is to develop an economical Demultiplexer for WDM
transmission over POF.
The main idea is to separate the chromatic light in its monochromatic
components with the help of a prism with low reciprocal dispersive power. The
prism and the other assemblies, which are needed to adjust the optical path,
should be manufactured in injection molding technique. This manufacturing
technique is a very simple and economical way to produce a mass production
applicable Demultiplexer for POF.Comment: 2006 International Students and Young Scientists Workshop "Photonics
and Microsystems
Hadronic unquenching effects in the quark propagator
We investigate hadronic unquenching effects in light quarks and mesons.
Within the non-perturbative continuum framework of Schwinger-Dyson and
Bethe-Salpeter equations we quantify the strength of the back reaction of the
pion onto the quark-gluon interaction. To this end we add a Yang-Mills part of
the interaction such that unquenched lattice results for various current quark
masses are reproduced. We find considerable effects in the quark mass function
at low momenta as well as for the chiral condensate. The quark wave function is
less affected. The Gell--Mann-Oakes-Renner relation is valid to good accuracy
up to pion masses of 400-500 MeV. As a byproduct of our investigation we verify
the Coleman theorem, that chiral symmetry cannot be broken spontaneously when
QCD is reduced to 1+1 dimensions.Comment: 27 pages, 15 figures, minor corrections and clarifications; version
to appear in PR
CHIRON - A Fiber Fed Spectrometer for Precise Radial Velocities
The CHIRON optical high-resolution echelle spectrometer was commissioned at
the 1.5m telescope at CTIO in 2011. The instrument was designed for high
throughput and stability, with the goal of monitoring radial velocities of
bright stars with high precision and high cadence for the discovery of low-mass
exoplanets. Spectral resolution of R=79,000 is attained when using a slicer
with a total (including telescope and detector) efficiency of 6% or higher,
while a resolution of R=136,000 is available for bright stars. A fixed spectral
range of 415 to 880 nm is covered. The echelle grating is housed in a vacuum
enclosure and the instrument temperature is stabilized to +-0.2deg. Stable
illumination is provided by an octagonal multimode fiber with excellent
light-scrambling properties. An iodine cell is used for wavelength calibration.
We describe the main optics, fiber feed, detector, exposure-meter, and other
aspects of the instrument, as well as the observing procedure and data
reduction.Comment: 15 pages, 10 figures. Accepted by PAS
Efficient Algorithm for Asymptotics-Based Configuration-Interaction Methods and Electronic Structure of Transition Metal Atoms
Asymptotics-based configuration-interaction (CI) methods [G. Friesecke and B.
D. Goddard, Multiscale Model. Simul. 7, 1876 (2009)] are a class of CI methods
for atoms which reproduce, at fixed finite subspace dimension, the exact
Schr\"odinger eigenstates in the limit of fixed electron number and large
nuclear charge. Here we develop, implement, and apply to 3d transition metal
atoms an efficient and accurate algorithm for asymptotics-based CI.
Efficiency gains come from exact (symbolic) decomposition of the CI space
into irreducible symmetry subspaces at essentially linear computational cost in
the number of radial subshells with fixed angular momentum, use of reduced
density matrices in order to avoid having to store wavefunctions, and use of
Slater-type orbitals (STO's). The required Coulomb integrals for STO's are
evaluated in closed form, with the help of Hankel matrices, Fourier analysis,
and residue calculus.
Applications to 3d transition metal atoms are in good agreement with
experimental data. In particular we reproduce the anomalous magnetic moment and
orbital filling of Chromium in the otherwise regular series Ca, Sc, Ti, V, Cr.Comment: 14 pages, 1 figur
Optical activation of germanium plasmonic antennas in the mid-infrared
Impulsive interband excitation with femtosecond near-infrared pulses establishes a plasma response in intrinsic germanium structures fabricated on a silicon substrate. This direct approach activates the plasmonic resonance of the Ge structures and enables their use as optical antennas up to the mid-infrared spectral range. The optical switching lasts for hundreds of picoseconds until charge recombination redshifts the plasma frequency. The full behavior of the structures is modeled by the electrodynamic response established by an electron-hole plasma in a regular array of antennas
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