305 research outputs found
Roles of the color antisymmetric ghost propagator in the infrared QCD
The results of Coulomb gauge and Landau gauge lattice QCD simulation do not
agree completely with continuum theory. There are indications that the ghost
propagator in the infrared region is not purely color diagonal as in high
energy region. After presenting lattice simulation of configurations produced
with Kogut-Susskind fermion (MILC collaboration) and those with domain wall
fermion (RBC/UKQCD collaboration), I investigate in triple gluon vertex and the
ghost-gluon-ghost vertex how the square of the color antisymmetric ghost
contributes. Then the effect of the vertex correction to the gluon propagator
and the ghost propagator is investigated.
Recent Dyson-Schwinger equation analysis suggests the ghost dressing function
finite and no infrared enhancement or . But the ghost
propagator renormalized by the loop containing a product of color antisymmetric
ghost is expected to behave as with
with , if the fixed point
scenario is valid. I interpret the solution should contain a
vertex correction. The infrared exponent of our lattice Landau gauge gluon
propagator of the RBC/UKQCD is and that of MILC is about
-0.7.
The implication for the Kugo-Ojima color confinement criterion, QCD effective
coupling and the Slavnov identity are given.Comment: 13 pages 10 figures, references added and revised. version to be
published in Few-Body System
Four-quark energies in SU(2) lattice Monte Carlo using a tetrahedral geometry
This contribution -- a continuation of earlier work -- reports on recent
developments in the calculation and understanding of 4-quark energies generated
using lattice Monte Carlo techniques.Comment: 3 pages, latex, no figures, contribution to Lattice 9
The asymmetry of the dimension 2 gluon condensate: the zero temperature case
We provide an algebraic study of the local composite operators A_\mu
A_\nu-\delta_{\mu\nu}/d A^2 and A^2, with d=4 the spacetime dimension. We prove
that these are separately renormalizable to all orders in the Landau gauge.
This corresponds to a renormalizable decomposition of the operator A_\mu A_\nu
into its trace and traceless part. We present explicit results for the relevant
renormalization group functions to three loop order, accompanied with various
tests of these results. We then develop a formalism to determine the zero
temperature effective potential for the corresponding condensates, and recover
the already known result for \neq 0, together with <A_\mu
A_\nu-\delta_{\mu\nu}/d A^2>=0, a nontrivial check that the approach is
consistent with Lorentz symmetry. The formalism is such that it is readily
generalizable to the finite temperature case, which shall allow a future
analytical study of the electric-magnetic symmetry of the condensate,
which received strong evidence from recent lattice simulations by Chernodub and
Ilgenfritz, who related their results to 3 regions in the Yang-Mills phase
diagram.Comment: 25 page
Pion wave functions from holographic QCD and the role of infrared renormalons in photon-photon collisions
In this article, we calculate the contribution of the higher-twist Feynman
diagrams to the large- inclusive single pion production cross section in
photon-photon collisions in case of the running coupling and frozen coupling
approaches within holographic QCD. We compare the resummed higher-twist cross
sections with the ones obtained in the framework of the frozen coupling
approach and leading-twist cross section. Also, we show that in the context of
frozen coupling approach a higher-twist contribution to the photon-photon
collisions cross section is normalized in terms of the pion electromagnetic
form factor.Comment: 21 pages, 15 figures. arXiv admin note: text overlap with
arXiv:0709.2072 by other author
Landau Gauge Fixing on GPUs
In this paper we present and explore the performance of Landau gauge fixing
in GPUs using CUDA. We consider the steepest descent algorithm with Fourier
acceleration, and compare the GPU performance with a parallel CPU
implementation. Using lattice volumes, we find that the computational
power of a single Tesla C2070 GPU is equivalent to approximately 256 CPU cores.Comment: 10 pages, 3 figures and 3 table
A Study of Degenerate Four-quark states in SU(2) Lattice Monte Carlo
The energies of four-quark states are calculated for geometries in which the
quarks are situated on the corners of a series of tetrahedra and also for
geometries that correspond to gradually distorting these tetrahedra into a
plane. The interest in tetrahedra arises because they are composed of {\bf
three } degenerate partitions of the four quarks into two two-quark colour
singlets. This is an extension of earlier work showing that geometries with
{\bf two} degenerate partitions (e.g.\ squares) experience a large binding
energy. It is now found that even larger binding energies do not result, but
that for the tetrahedra the ground and first excited states become degenerate
in energy. The calculation is carried out using SU(2) for static quarks in the
quenched approximation with on a lattice. The
results are analysed using the correlation matrix between different euclidean
times and the implications of these results are discussed for a model based on
two-quark potentials.Comment: Original Raw PS file replace by a tarred, compressed and uuencoded PS
fil
The reaction ppbar -> Lambda_c-Lambda_cbar close to threshold
Predictions for the charm-production reaction antiproton-proton ->
antiLambda_c-Lambda_c for energies near the threshold are presented. The
calculations are performed in a meson-exchange framework in close analogy to
our earlier study on antiproton-proton -> antiLambda-Lambda by connecting the
two processes via SU(4) symmetry. The obtained antiLambda_c-Lambda_c production
cross sections are in the order of 1 to 7 \mub, i.e. a factor of around 10
smaller than the corresponding cross sections for antiLambda-Lambda. However,
they are 100 to 1000 times larger than predictions of other model calculations
in the literature.Comment: 12 pages, 4 figure
Effects of Symmetry Breaking on the Strong and Electroweak Interactions of the Vector Nonet
Starting from a chiral invariant and quark line rule conserving Lagrangian of
pseudoscalar and vector nonets we introduce first and second order symmetry
breaking as well as quark line rule violating terms and fit the parameters, at
tree level, to many strong and electroweak processes. A number of predictions
are made. The electroweak interactions are included in a manifestly gauge
invariant manner. The resulting symmetry breaking pattern is discussed in
detail. Specifically, for the ``strong'' interactions, we study all the vector
meson masses and V -> \phi \phi decays, including isotopic spin violations. In
the electroweak sector we study the { rho^0 , omega , phi } -> e^+e^- decays, {
pi^+ , K^+ , K^0 } ``charge radii'', K_{l3} ``slope factor'' and the overall
e^+e^- -> pi^+ pi^- process. It is hoped that the resulting model may be useful
as a reasonable description of low energy physics in the range up to about 1
GeV.Comment: 43 pages (LaTeX), 5 PostScript figures are included as
uuencoded-compressed-tar file at the en
Class-Discriminative Weighted Distortion Measure for VQ-based Speaker Identification
We consider the distortion measure in vector quantization based speaker identification system. The model of a speaker is a codebook generated from the set of feature vectors from the speakers voice sample. The matching is performed by evaluating the distortions between the unknown speech sample and the models in the speaker database. In this paper, we introduce a weighted distortion measure that takes into account the correlations between the known models in the database. Larger weights are assigned to vectors that have high discriminating power between the speakers and vice versa
Renormalizability of a quark-gluon model with soft BRST breaking in the infrared region
We prove the renormalizability of a quark-gluon model with a soft breaking of
the BRST symmetry, which accounts for the modification of the large distance
behavior of the quark and gluon correlation functions. The proof is valid to
all orders of perturbation theory, by making use of softly broken Ward
identities.Comment: 20 pages, no figures. Preprint number added in v2
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