2,351 research outputs found
Finite ma corrections for sea quark matrix elements
We discuss the finite corrections associated with the computation of sea
quark matrix elements. We find them to differ from the standard normalization
used for valence quarks and to depend strongly on the Lorentz structure of the
current under consideration. Phenomenological implications of these results are
briefly discussed in two examples. We also mention how the magnitude of the
correction factors can be reduced by using a 2-link improved action.Comment: 3 pages, contribution to LATTICE'94, uuencoded compressed tar file
(square root removed in equation (1)
Flavor-Symmetry Restoration and Symanzik Improvement for Staggered Quarks
We resolve contradictions in the literature concerning the origins and size
of unphysical flavor-changing strong interactions generated by the
staggered-quark discretization of QCD. We show that the leading contributions
are tree-level in \order(a^2) and that they can be removed by adding three
correction terms to the link operator in the standard action. These corrections
are part of the systematic Symanzik improvement of the staggered-quark action.
We present a new improved action for staggered quarks that is accurate up to
errors of \order(a^4,a^2\alpha_s) --- more accurate than most, if not all,
other discretizations of light-quark dynamics.Comment: 7 page
The Quenched Continuum Limit
We show that all current formalisms for quarks in lattice QCD are consistent
in the quenched continuum limit, as they should be. We improve on previous
extrapolations to this limit, and the understanding of lattice systematic
errors there, by using a constrained fit including both leading and sub-leading
dependence on a.Comment: Poster presented at Lattice2004(spectrum), Fermilab, June 21-26, 200
Meson Decay Constants from the Valence Approximation to Lattice QCD
We evaluate , , , and , extrapolated to physical quark mass, zero
lattice spacing and infinite volume, for lattice QCD with Wilson quarks in the
valence (quenched) approximation. The predicted ratios differ from experiment
by amounts ranging from 12\% to 17\% equivalent to between 0.9 and 2.8 times
the corresponding statistical uncertainties.Comment: uufiles encoded copy of 40 page Latex article, including 14 figures
in Postscript. The long version of hep-lat/9302012, IBM/HET 93-
String Tension and Thermodynamics with Tree Level and Tadpole Improved Actions
We calculate the string tension, deconfinement transition temperature and
bulk thermodynamic quantities of the SU(3) gauge theory using tree level and
tadpole improved actions. Finite temperature calculations have been performed
on lattices with temporal extent N_tau = 3 and 4. Compared to calculations with
the standard Wilson action on this size lattices we observe a drastic reduction
of the cut-off dependence of bulk thermodynamic observables at high
temperatures. In order to test the influence of improvement on long-distance
observables at T_c we determine the ratio T_c/sqrt(sigma). For all actions,
including the standard Wilson action, we find results which differ only little
from each other. We do, however, observe an improved asymptotic scaling
behaviour for the tadpole improved action compared to the Wilson and tree level
improved actions.Comment: 20 pages, LaTeX2e File, 8 coloured Postscript figures, new analysis
added, recent Wilson action string tension results included, figures replace
Improving the staggered quark action to reduce flavour symmetry violations
We investigate a class of actions for lattice QCD with staggered quarks aimed
at reducing the flavour symmetry violations associated with using staggered
fermions. These actions replace the gauge field link fields in the quark action
with covariantly smeared fields. As such they are an extension of actions
considered by the MILC collaboration. We show that such actions systematically
reduce flavour symmetry violations in the weak coupling limit. Using the mass
splitting between Goldstone and non-Goldstone pions as a measure of flavour
symmetry violations we find that these actions have considerably less flavour
symmetry violations than the standard staggered action, and represent an
improvement on what can be achieved with the MILC action, on quenched
configurations with .Comment: 3 pages, Latex using espcrc2.sty. 1 coloured postscript figure
included with epsffile. Talk presented by D.K.Sinclair at LATTICE'97,
Edinburgh, Scotlan
Perturbative expansions from Monte Carlo simulations at weak coupling: Wilson loops and the static-quark self-energy
Perturbative coefficients for Wilson loops and the static-quark self-energy
are extracted from Monte Carlo simulations at weak coupling. The lattice
volumes and couplings are chosen to ensure that the lattice momenta are all
perturbative. Twisted boundary conditions are used to eliminate the effects of
lattice zero modes and to suppress nonperturbative finite-volume effects due to
Z(3) phases. Simulations of the Wilson gluon action are done with both periodic
and twisted boundary conditions, and over a wide range of lattice volumes (from
to ) and couplings (from to ).
A high precision comparison is made between the simulation data and results
from finite-volume lattice perturbation theory. The Monte Carlo results are
shown to be in excellent agreement with perturbation theory through second
order. New results for third-order coefficients for a number of Wilson loops
and the static-quark self-energy are reported.Comment: 36 pages, 15 figures, REVTEX documen
On the Size of Hadrons
The form factor and the mean-square radius of the pion are calculated
analytically from a parametrized form of a wave function. The
numerical wave function was obtained previously by solving numerically an
eigenvalue equation for the pion in a particular model. The analytical formulas
are of more general interest than just be valid for the pion and can be
generalized to the case with unequal quark masses. Two different
parametrizations are investigated. Because of the highly relativistic problem,
noticable deviations from a non-relativistic formula are obtained.Comment: 14 pages, minor typos corrected, several points clarified, results
unchange
Search for Lambda^2/p^2 corrections to the QCD running coupling
We investigate the occurrence of power terms in the running
QCD coupling by analysing non-perturbative measurements of at
quite low momenta obtained from the lattice three-gluon vertex. Our study
provides some evidence for such a contribution. The phenomenological
implications of such a presence are reviewed.Comment: 3 pages, 1 figure, LaTeX, LATTICE98(Confinement
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