3,514 research outputs found
Nonperturbative ``Lattice Perturbation Theory''
We discuss a program for replacing standard perturbative methods with Monte
Carlo simulations in short distance lattice gauge theory calculations.Comment: 3 pages, uuencoded Latex file, two embedded figures and .sty file
include
Moving NRQCD for B Form Factors at High Recoil
We derive the continuum and lattice tree-level moving NRQCD (mNRQCD) through
order 1/m^2. mNRQCD is a generalization of NRQCD for dealing with hadrons with
nonzero velocity u_mu. The quark's total momentum is written as P^mu=Mu^mu+k^mu
where k^mu << Mu^mu is discretized and Mu^mu is treated exactly. Radiative
corrections to couplings on the lattice are discussed. mNRQCD is particularly
useful for calculating B->pi and B->D form factors since errors are similar at
low and high recoil.Comment: 3 pages, 1 figure, Lattice2002(heavyquark
Improving lattice perturbation theory
Lepage and Mackenzie have shown that tadpole renormalization and systematic
improvement of lattice perturbation theory can lead to much improved numerical
results in lattice gauge theory. It is shown that lattice perturbation theory
using the Cayley parametrization of unitary matrices gives a simple analytical
approach to tadpole renormalization, and that the Cayley parametrization gives
lattice gauge potentials gauge transformations close to the continuum form. For
example, at the lowest order in perturbation theory, for SU(3) lattice gauge
theory, at the `tadpole renormalized' coupling to be compared to the non-perturbative numerical value Comment: Plain TeX, 8 page
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
On the Viability of Lattice Perturbation Theory
In this paper we show that the apparent failure of QCD lattice perturbation
theory to account for Monte Carlo measurements of perturbative quantities
results from choosing the bare lattice coupling constant as the expansion
parameter. Using instead ``renormalized'' coupling constants defined in terms
of physical quantities, like the heavy-quark potential, greatly enhances the
predictive power of lattice perturbation theory. The quality of these
predictions is further enhanced by a method for automatically determining the
coupling-constant scale most appropriate to a particular quantity. We present a
mean-field analysis that explains the large renormalizations relating lattice
quantities, like the coupling constant, to their continuum analogues. This
suggests a new prescription for designing lattice operators that are more
continuum-like than conventional operators. Finally, we provide evidence that
the scaling of physical quantities is asymptotic or perturbative already at
's as low as 5.7, provided the evolution from scale to scale is analyzed
using renormalized perturbation theory. This result indicates that reliable
simulations of (quenched) QCD are possible at these same low 's.Comment: 3
Pion Form Factor in the Factorization Formalism
Based on the light-cone (LC) framework and the factorization formalism,
the transverse momentum effects and the different helicity components'
contributions to the pion form factor are recalculated. In
particular, the contribution to the pion form factor from the higher helicity
components (), which come from the spin-space Wigner
rotation, are analyzed in the soft and hard energy regions respectively. Our
results show that the right power behavior of the hard contribution from the
higher helicity components can only be obtained by fully keeping the
dependence in the hard amplitude, and that the dependence in LC wave
function affects the hard and soft contributions substantially. As an example,
we employ a model LC wave function to calculate the pion form factor and then
compare the numerical predictions with the experimental data. It is shown that
the soft contribution is less important at the intermediate energy region.Comment: 21 pages, 4 figure
DEPENDENCE OF THE CURRENT RENORMALISATION CONSTANTS ON THE QUARK MASS
We study the behaviour of the vector and axial current renormalisation
constants and as a function of the quark mass, . We show that
sizeable and systematic effects are present in the
Wilson and Clover cases respectively. We find that the prescription of
Kronfeld, Lepage and Mackenzie for correcting these artefacts is not always
successful.Comment: Contribution to Lattice'94, 3 pages PostScript, uuencoded compressed
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