75 research outputs found
Scaling Properties of the Probability Distribution of Lattice Gribov Copies
We study the problem of the Landau gauge fixing in the case of the SU(2)
lattice gauge theory. We show that the probability to find a lattice Gribov
copy increases considerably when the physical size of the lattice exceeds some
critical value , almost independent of the lattice
spacing. The impact of the choice of the copy on Green functions is presented.
We confirm that the ghost propagator depends on the choice of the copy, this
dependence decreasing for increasing volumes above the critical one. The gluon
propagator as well as the gluonic three-point functions are insensitive to
choice of the copy (within present statistical errors). Finally we show that
gauge copies which have the same value of the minimisation functional () are equivalent, up to a global gauge transformation, and
yield the same Green functions.Comment: replaced with revised version; 23 pages, 7 figures, 27 table
Gluon propagator, triple gluon vertex and the QCD coupling constant
We study the UV-scaling of the flavorless gluon propagator in the Landau
gauge in an energy window up to 9 GeV. Dominant hypercubic lattice artifacts
are eliminated. A large set of renormalization schemes is used to test
asymptotic scaling. We compare with our results obtained directly from the
triple gluon vertex. We end-up with \Lambda_{\bar{\rm{MS}}} = 318(12)(5) MeV
and 292(5)(15) MeV respectively for these two methods, compatible which each
other but significantly above the Schrodinger method estimate.Comment: 3 pages, LaTeX with two figures; presented at LATTICE9
Nuclear models on a lattice
We present the first results of a quantum field approach to nuclear models
obtained by lattice techniques. Renormalization effects for fermion mass and
coupling constant in case of scalar and pseudoscalar interaction lagrangian
densities are discussed.Comment: 4 pages - 7 figures ; Invited talk to QCD 05: 12th International QCD
Conference, 4-9 Jul 2005, Montpellier, France ; To appear in Nucl. Phys. B
(Proc. Suppl.
On AdS/QCD correspondence and the partonic picture of deep inelastic scattering
We critically examine the question of scaling of the Deep Inelastic
Scattering process in the medium Bjorken x region on a scalar boson in the
framework of the AdS/QCD correspondence. To get the right polarization
structure of the forward electroproduction amplitude, we show that one needs to
add (at least) the scalar to scalar and scalar to vector hadronic amplitudes.
This illustrates how the partonic picture may emerge from a simple scenario
based on the AdS/QCD correspondence, provided one allows the conformal
dimension of the hadronic field to equal 1 and use the concept of "hadron -
parton duality" .Comment: Second version with a few added clarifications and references. Third
version with a misprint corrected in Eq. 35 and following unnumbered
equation; to appear in Physics Letters
Finite energy/action solutions of Yang-Mills equations on Schwarzschild and deSitter backgrounds for dimension
Physically relevant gauge and gravitational theories can be seen as special
members of hierarchies of more elaborate systems. The Yang-Mills (YM) system is
the first member of a hierarchy of Lagrangians which we will index by ,
and the Einstein-Hilbert (EH) system of general relativity is the first member
of another hierarchy which we index by . In this paper, we study the
classical equations of the YM hierarchy considered in the
background of special geometries (Schwarzschild, deSitter,anti-deSitter) of the
EH hierarchy. Solutions are obtained in various dimensions and lead
to several examples of non-self-dual YM fields. When self-dual
solutions exist in addition. Their action is equal to the Chern-Pontryagin
charge and can be compared with that of the non-self-dual solutions.Comment: LaTeX, 25 pages, 2 figures, new title, minor change
The Infrared Behaviour of the Pure Yang-Mills Green Functions
We study the infrared behaviour of the pure Yang-Mills correlators using
relations that are well defined in the non-perturbative domain. These are the
Slavnov-Taylor identity for three-gluon vertex and the Schwinger-Dyson equation
for ghost propagator in the Landau gauge. We also use several inputs from
lattice simulations. We show that lattice data are in serious conflict with a
widely spread analytical relation between the gluon and ghost infrared critical
exponents. We conjecture that this is explained by a singular behaviour of the
ghost-ghost-gluon vertex function in the infrared. We show that, anyhow, this
discrepancy is not due to some lattice artefact since lattice Green functions
satisfy the ghost propagator Schwinger-Dyson equation. We also report on a
puzzle concerning the infrared gluon propagator: lattice data seem to favor a
constant non vanishing zero momentum gluon propagator, while the Slavnov-Taylor
identity (complemented with some regularity hypothesis of scalar functions)
implies that it should diverge.Comment: 25 pages, 7 figures; replaced version with some references adde and
an enlarged discussion of the non-renormalization theorem; second replacement
with improved figures and added reference
Lattice calculation of corrections to and of in the scheme
We report on very strong evidence of the occurrence of power terms in
\as(p), the QCD running coupling constant in the scheme, by
analyzing non-perturbative measurements from the lattice three-gluon vertex
between 2.0 and 10.0 GeV at zero flavor. While putting forward the caveat that
this definition of the coupling is a gauge dependent one, the general relevance
of such an occurrence is discussed. We fit MeV in perfect agreement with the result obtained by
the ALPHA group with a totally different method.
The power correction to \as(p) is fitted to .Comment: 21 pages, 3 figure
Asymptotic behavior of the ghost propagator in SU3 lattice gauge theory
We study the asymptotic behavior of the ghost propagator in the quenched
SU(3) lattice gauge theory with Wilson action. The study is performed on
lattices with a physical volume fixed around 1.6 fm and different lattice
spacings: 0.100 fm, 0.070 fm and 0.055 fm. We implement an efficient algorithm
for computing the Faddeev-Popov operator on the lattice. We are able to
extrapolate the lattice data for the ghost propagator towards the continuum and
to show that the extrapolated data on each lattice can be described up to
four-loop perturbation theory from 2.0 GeV to 6.0 GeV. The three-loop values
are consistent with those extracted from previous perturbative studies of the
gluon propagator. However the effective \Lambda_{\ms} scale which reproduces
the data does depend strongly upon the order of perturbation theory and on the
renormalization scheme used in the parametrization. We show how the truncation
of the perturbative series can account for the magnitude of the dependency in
this energy range. The contribution of non-perturbative corrections will be
discussed elsewhere.Comment: 26 pages, 7 figure
- …