40 research outputs found
SSOR preconditioning in simulations of the QCD Schr\"odinger functional
We report on a parallelized implementation of SSOR preconditioning for O(a)
improved lattice QCD with Schr\"odinger functional boundary conditions.
Numerical simulations in the quenched approximation at parameters in the light
quark mass region demonstrate that a performance gain of a factor 1.5
over even-odd preconditioning can be achieved.Comment: 15 pages, latex2e, 4 Postscript figures, uses packages elsart and
epsfi
Renormalization group invariant average momentum of non-singlet parton densities
We compute, within the Schr\"odinger functional scheme, a renormalization
group invariant renormalization constant for the first moment of the
non-singlet parton distribution function. The matching of the results of our
non-perturbative calculation with the ones from hadronic matrix elements allows
us to obtain eventually a renormalization group invariant average momentum of
non-singlet parton densities, which can be translated into a preferred scheme
at a specific scale.Comment: Latex2e file, 4 figures, 12 page
Monte Carlo determination of the critical coupling in theory
We use lattice formulation of theory in order to investigate
non--perturbative features of its continuum limit in two dimensions. In
particular, by means of Monte Carlo calculations, we obtain the critical
coupling constant in the continuum, where is the {\em
unrenormalised} coupling. Our final result is .Comment: Version published on Phys. Rev. D. We added a reference and modified
a couple of sentence
f_B and two scales problems in lattice QCD
A novel method to calculate f_B on the lattice is introduced, based on the
study of the dependence of finite size effects upon the heavy quark mass of
flavoured mesons and on a non-perturbative recursive finite size technique. We
avoid the systematic errors related to extrapolations from the static limit or
to the tuning of the coefficients of effective Lagrangian and the results admit
an extrapolation to the continuum limit. We perform a first estimate at finite
lattice spacing, but close to the continuum limit, giving f_B = 170(11)(5)(22)
MeV. We also obtain f_{B_s} = 192(9)(5)(24) MeV. The first error is
statistical, the second is our estimate of the systematic error from the method
and the third the systematic error from the specific approximations adopted in
this first exploratory calculation. The method can be generalized to two--scale
problems in lattice QCD.Comment: 16 pages, 5 figures. Accepted for publication by Phys.Lett.B. Revised
version, discussion on systematic errors added, results unchange
Universal continuum limit of non-perturbative lattice non-singlet moment evolution
We present evidence for the universality of the continuum limit of the scale
dependence of the renormalization constant associated with the operator
corresponding to the average momentum of non-singlet parton densities. The
evidence is provided by a non-perturbative computation in quenched lattice QCD
using the Schr\"odinger Functional scheme. In particular, we show that the
continuum limit is independent of the form of the fermion action used, i.e. the
Wilson action and the non-perturbatively improved clover action.Comment: Latex2e file, 2 figures, 9 page
Low energy physics from the QCD Schr\"odinger functional
We review recent work by the ALPHA and UKQCD Collaborations where masses and
matrix elements were computed in lattice QCD using Schr\"odinger functional
boundary conditions and where the strange quark mass was determined in the
quenched approximation. We emphasize the general concepts and our strategy for
the computation of quark masses.Comment: Talks at LATTICE99 (QCD Spectrum and Quark Masses), 5 pages, latex2e,
5 Postscript figures, uses epsfig, amssymb and espcrc
Non-perturbative results for the coefficients b_m and b_a-b_p in O(a) improved lattice QCD
We determine the improvement coefficients b_m and b_a-bp in quenched lattice
QCD for a range of beta-values, which is relevant for current large scale
simulations. At fixed beta, the results are rather sensitive to the precise
choices of parameters. We therefore impose improvement conditions at constant
renormalized parameters, and the coefficients are then obtained as smooth
functions of g_0^2. Other improvement conditions yield a different functional
dependence, but the difference between the coefficients vanishes with a rate
proportional to the lattice spacing. We verify this theoretical expectation in
a few examples and are therefore confident that O(a) improvement is achieved
for physical quantities. As a byproduct of our analysis we also obtain the
finite renormalization constant which relates the subtracted bare quark mass to
the bare PCAC mass.Comment: 25 pages, 8 figures, minor change at figure