297 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
Infrared features of unquenched finite temperature lattice Landau gauge QCD
The color diagonal and color antisymmetric ghost propagators slightly above
of MILC lattices are measured and compared with
zero temperature unquenched MILC and MILC
lattices and zero temperature quenched and
6.45 lattices. The expectation value of the color antisymmetric ghost
propagator is zero but its Binder cumulant, which is consistent
with that of dimensional Gaussian distribution below , decreases
above . Although the color diagonal ghost propagator is temperature
independent, the norm of the color antisymmetric ghost propagator is
temperature dependent. The expectation value of the ghost condensate observed
at zero temperature unquenched configuration is consistent with 0 in .
We also measure transverse, magnetic and electric gluon propagator and
extract gluon screening masses. The running coupling measured from the product
of the gluon dressing function and the ghost dressing function are almost
temperature independent but the effect of condensate observed at zero
temperature is consistent with 0 in .
The transverse gluon dressing function at low temperature has a peak in the
infrared but it becomes flatter at high temperature. Its absolute value in the
high momentum is larger for high temperature and similar to the magnetic gluon
dressing function. The electric gluon propagator at high momentum is
temperature independent. These data imply that the magnetic gluon propagator
and the color antisymmetric ghost propagator are affected by the presence of
dynamical quarks and there are strong non-perturbative effects through the
temperature dependent color anti-symmetric ghost propagator.Comment: 11 pages 16 figures, version accepted for publication in Phys. Rev.
Numerical Study of the Ghost-Gluon Vertex in Landau gauge
We present a numerical study of the ghost-gluon vertex and of the
corresponding renormalization function \widetilde{Z}_1(p^2) in minimal Landau
gauge for SU(2) lattice gauge theory. Data were obtained for three different
lattice volumes (V = 4^4, 8^4, 16^4) and for three lattice couplings \beta =
2.2, 2.3, 2.4. Gribov-copy effects have been analyzed using the so-called
smeared gauge fixing. We also consider two different sets of momenta (orbits)
in order to check for possible effects due to the breaking of rotational
symmetry. The vertex has been evaluated at the asymmetric point (0;p,-p) in
momentum-subtraction scheme. We find that \widetilde{Z}_1(p^2) is approximately
constant and equal to 1, at least for momenta p > ~ 1 GeV. This constitutes a
nonperturbative verification of the so-called nonrenormalization of the Landau
ghost-gluon vertex. Finally, we use our data to evaluate the running coupling
constant \alpha_s(p^2).Comment: 19 pages, 6 figures, 9 tables, using axodraw.sty; minor modifications
in the abstract, introduction and conclusion
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
The magnetic mass of transverse gluon, the B-meson weak decay vertex and the triality symmetry of octonion
With an assumption that in the Yang-Mills Lagrangian, a left-handed fermion
and a right-handed fermion both expressed as quaternion make an octonion which
possesses the triality symmetry, I calculate the magnetic mass of the
transverse self-dual gluon from three loop diagram, in which a heavy quark pair
is created and two self-dual gluons are interchanged.
The magnetic mass of the transverse gluon depends on the mass of the pair
created quarks, and in the case of charmed quark pair creation, the magnetic
mass becomes approximately equal to at MeV. A possible time-like magnetic gluon mass
from two self-dual gluon exchange is derived, and corrections in the B-meson
weak decay vertices from the two self-dual gluon exchange are also evaluated.Comment: 22 pages, 9 figure
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
Infrared Features of the Landau Gauge QCD
The infrared features of Landau gauge QCD are studied by the lattice
simulation of and . We
adopt two definitions of the gauge field; 1) linear 2) and
measured the gluon propagator and ghost propagator. Infrared singularity of the
gluon propagator is less than that of tree level result but the gluon
propagator at 0 momentum remains finite. The infrared singularity of ghost
propagator is stronger than the tree level. The QCD running coupling measured
by using the gluon propagator and the ghost propagator has a maximum
at around and decreases as approaches 0.
The data are analyzed in use of formula of the principle of minimal
sensitivity(PMS), the effective charge method and the contour-improved
perturbation method, which suggest necessity of the resummation of perturbation
series in the infrared region together with existence of the infrared fixed
point. Kugo-Ojima parameter saturates at about -0.8 in contrast to the
theoretically expected value -1.Comment: RevTex4, 9 pages, 10 eps figures, Typos corrected. To be published in
Phys. Rev. D(2004
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
The Gribov problem and QCD dynamics
In 1967, Faddeev and Popov were able to quantize the Yang-Mills theory by
introducing new particles called ghost through the introduction of a gauge.
Ever since, this quantization has become a standard textbook item. Some years
later, Gribov discovered that the gauge fixing was not complete, gauge copies
called Gribov copies were still present and could affect the infrared region of
quantities like the gauge dependent gluon and ghost propagator. This feature
was often in literature related to confinement. Some years later, the
semi-classical approach of Gribov was generalized to all orders and the
so-called GZ action was born. Ever since, many related articles were published.
This review tends to give a pedagogic review of the ideas of Gribov and the
subsequent construction of the GZ action, including many other toipics related
to the Gribov region. It is shown how the GZ action can be viewed as a
non-perturbative tool which has relations with other approaches towards
confinement. Many different features related to the GZ action shall be
discussed in detail, such as BRST breaking, the KO criterion, the propagators,
etc. We shall also compare with the lattice data and other non-perturbative
approaches, including stochastic quantization.Comment: 121 pages, 12 figures, Review article, references adde
A two-component picture of the <A^2> condensate with instantons
We study the interplay between the condensate and instantons in
non-Abelian gauge theory. Therefore we use the formalism of Local Composite
Operators, with which the vacuum expectation value of this condensate can be
analytically computed. We first use the dilute gas approximation and partially
solve the infrared problem of instanton physics. In order to find quantitative
results, however, we turn to an instanton liquid model, where we find how the
different contributions to the condensate add up.Comment: 9 pages, 1 figur
- …