4,606 research outputs found
On the Analytic Structure of the Quark Self-Energy in Nambu-Jona- Lasinio Models
The self-energy of quarks is investigated for various models which are
inspired by the Nambu--Jona-Lasinio (NJL) model. Including, beyond the
Hartree-Fock approximation, terms up to second-order in the quark interaction,
the real and imaginary parts of scalar and vector components of the self-energy
are discussed. The second-order contributions depend on the energy and momentum
of the quark under consideration. This leads to solutions of the Dirac equation
which are significantly different from those of a free quark or a quark with
constant effective mass, as obtained in the Hartree-Fock approximation.Comment: 15 pages LaTeX, 6 figures can be obtained from author
Combinatorial Solutions to Normal Ordering of Bosons
We present a combinatorial method of constructing solutions to the normal
ordering of boson operators. Generalizations of standard combinatorial notions
- the Stirling and Bell numbers, Bell polynomials and Dobinski relations - lead
to calculational tools which allow to find explicitly normally ordered forms
for a large class of operator functions.Comment: Presented at 14th Int. Colloquium on Integrable Systems, Prague,
Czech Republic, 16-18 June 2005. 6 pages, 11 reference
Studies on growth rates in pigs and the effect of birth weight
End of project reportThe purpose of this study was to assess some environmental and management factors that affect growth performance on commercial pig units. In experiment 1, a survey was carried out on 22 pig units of known growth performance in south-west Ireland to compare management factors between those showing poor and good growth rates. Low growth rate appears to be due to the cumulative effect of a combination of factors. Experiment 2 was conducted to determine the effects of providing an
additional feeder on performance of weaned piglets. No benefits were
recorded. Feed consumed from the additional feeder was a replacement for
feed that otherwise would have been consumed from the control hopper
feeder.
Experiment 3 was designed to determine if pig performance and efficiency of
growth were affected by weight at birth and at weaning. Lightweight pigs
showed inferior growth performance up to the finisher period. Although they
compensated some of the inferior growth towards the time of slaughter, they
never reached the weights of the heavy birth-weight animals. Males were
either significantly heavier or tended to be heavier than females throughout.
There was no significant difference between the sexes in the number of days
to slaughter. Light and heavy pigs did not differ in the levels of IGF-1 in their
blood plasma; however lightweight pigs had significantly lower IgG preweaning.
Experiment 4 aimed to determine whether piglet birth weight influenced
growth performance, plasma IGF-1 concentrations and muscle fibre
characteristics at day 42 of life. At slaughter (Day 42) light birth weight pigs
were significantly (P < 0.001) lighter. Plasma IGF-1 concentration was lower
by 28% (P=0.06) in light pigs. Muscle fibre cross sectional area and total fibre
number were not significantly different between groups. This study should be
repeated with bigger numbers
Diquarks: condensation without bound states
We employ a bispinor gap equation to study superfluidity at nonzero chemical
potential: mu .neq. 0, in two- and three-colour QCD. The two-colour theory,
QC2D, is an excellent exemplar: the order of truncation of the quark-quark
scattering kernel: K, has no qualitative impact, which allows a straightforward
elucidation of the effects of mu when the coupling is strong. In rainbow-ladder
truncation, diquark bound states appear in the spectrum of the three-colour
theory, a defect that is eliminated by an improvement of K. The corrected gap
equation describes a superfluid phase that is semi-quantitatively similar to
that obtained using the rainbow truncation. A model study suggests that the
width of the superfluid gap and the transition point in QC2D provide reliable
quantitative estimates of those quantities in QCD.Comment: 7 pages, 3 figures, REVTEX, epsfi
Suppression of stimulated Brillouin scattering in optical fibers using a linearly chirped diode laser
The output of high power fiber amplifiers is typically limited by stimulated Brillouin scattering (SBS). An analysis of SBS with a chirped pump laser indicates that a chirp of 2.5 Ă— 10^(15) Hz/s could raise, by an order
of magnitude, the SBS threshold of a 20-m fiber. A diode laser with a constant output power and a linear chirp of 5 Ă— 10^(15) Hz/s has been previously demonstrated. In a low-power proof-of-concept experiment, the threshold for SBS in a 6-km fiber is increased by a factor of 100 with a
chirp of 5 Ă— 10^(14) Hz/s. A linear chirp will enable straightforward coherent combination of multiple fiber amplifiers, with electronic compensation of path length differences on the order of 0.2 m
Aspects and consequences of a dressed-quark-gluon vertex
Features of the dressed-quark-gluon vertex and their role in the gap and
Bethe-Salpeter equations are explored. It is argued that quenched lattice data
indicate the existence of net attraction in the colour-octet projection of the
quark-antiquark scattering kernel. This attraction affects the uniformity with
which solutions of truncated equations converge pointwise to solutions of the
complete gap and vertex equations. For current-quark masses less than the scale
set by dynamical chiral symmetry breaking, the dependence of the
dressed-quark-gluon vertex on the current-quark mass is weak. The study employs
a vertex model whose diagrammatic content is explicitly enumerable. That
enables the systematic construction of a vertex-consistent Bethe-Salpeter
kernel and thereby an exploration of the consequences for the strong
interaction spectrum of attraction in the colour-octet channel. With rising
current-quark mass the rainbow-ladder truncation is shown to provide an
increasingly accurate estimate of a bound state's mass. Moreover, the
calculated splitting between vector and pseudoscalar meson masses vanishes as
the current-quark mass increases, which argues for the mass of the pseudoscalar
partner of the \Upsilon(1S) to be above 9.4 GeV. The absence of
colour-antitriplet diquarks from the strong interaction spectrum is contingent
upon the net amount of attraction in the octet projected quark-antiquark
scattering kernel. There is a window within which diquarks appear. The amount
of attraction suggested by lattice results is outside this domain.Comment: 22 pages, 12 figure
Can a Logarithmically Running Coupling Mimic a String Tension?
It is shown that a Coulomb potential using a running coupling slightly
modified from the perturbative form can produce an interquark potential that
appears nearly linear over a large distance range. Recent high-statistics SU(2)
lattice gauge theory data fit well to this potential without the need for a
linear string-tension term. This calls into question the accuracy of string
tension measurements which are based on the assumption of a constant
coefficient for the Coulomb term. It also opens up the possibility of obtaining
an effectively confining potential from gluon exchange alone.Comment: 13 pages, LaTeX, two figures not included, available from author.
revision - Line lengths fixed so it will tex properl
Remote state preparation and teleportation in phase space
Continuous variable remote state preparation and teleportation are analyzed
using Wigner functions in phase space. We suggest a remote squeezed state
preparation scheme between two parties sharing an entangled twin beam, where
homodyne detection on one beam is used as a conditional source of squeezing for
the other beam. The scheme works also with noisy measurements, and provide
squeezing if the homodyne quantum efficiency is larger than 50%. Phase space
approach is shown to provide a convenient framework to describe teleportation
as a generalized conditional measurement, and to evaluate relevant degrading
effects, such the finite amount of entanglement, the losses along the line, and
the nonunit quantum efficiency at the sender location.Comment: 2 figures, revised version to appear in J.Opt.
Characterization of the Hamamatsu R11410-10 3-Inch Photomultiplier Tube for Liquid Xenon Dark Matter Direct Detection Experiments
To satisfy the requirements of the next generation of dark matter detectors
based on the dual phase TPC, Hamamatsu, in close collaboration with UCLA, has
developed the R11410-10 photomultipler tube. In this work, we present the
detailed tests performed on this device. High QE (>30%) accompanied by a low
dark count rate (50 Hz at 0.3 PE) and high gain (10^7) with good single PE
resolution have been observed. A comprehensive screening measurement campaign
is ongoing while the manufacturer quotes a radioactivity of 20 mBq/PMT. These
characteristics show the R11410-10 to be particularly suitable for the
forthcoming zero background liquid xenon detectors.Comment: 19 pages, 18 figure
The Calculation of Vacuum Properties from the Global Color Symmetry Model
A modified method for calculating the non-perturbative quark vacuum
condensates from the global color symmetry model is derived. Within this
approach it is shown that the vacuum condensates are free of ultraviolet
divergence which is different from previous studies. As a special, the
two-quark condensate and the mixed quark-gluon condensate are calculated. A
comparision with the results of the other nonperturbative QCD approaches is
given.Comment: 17 page
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