1,246 research outputs found
Determining gA using non-perturbatively O(a) improved Wilson fermions
A completely non-perturbative estimate is given for gA using both quenched
and unquenched O(a) improved Wilson fermions. Particular attention is paid to
the determination of the axial renormalisation constant, ZA, using the Ward
identity for the propagator. For the quenched case, we have results at three
lattice spacings allowing a continuum extrapolation.Comment: Lattice 2000 (Hadronic Matrix Elements), 4 page
QCD Sum Rules on the Lattice
We study the work of Leinweber by applying the Continuum Model of QCD Sum
Rules (QCDSR) to the analysis of (quenched) lattice correlation functions. We
expand upon his work in several areas and find that, while the QCDSR Continuum
Model very adequately fits lattice data, it does so only for non-physical
values of its parameters. The non-relativistic model is found to predict
essentially the same form for the correlation functions as the QCDSR Continuum
Model but without the latter's restrictions. By fitting lattice data to a
general form which includes the non-relativistic quark model as a special case,
we confirm it as the model of choice.Comment: Talk presented by C.R. Allton at LAT97, Edinburgh. 3 pages, uses
espcrc2.st
Improved non-perturbative renormalization without
Recently, a method for O(a) improvement of composite operators has been
proposed which uses the large momentum behavior of fixed gauge quark and gluon
correlation functions (G. Martinelli et al., hep-lat/0106003). A practical
problem with this method is that a particular improvement coefficient,
, which has a gauge non-covariant form, is difficult to determine.
Here I work out the size of the errors made in improvement coefficients and
physical quantities if one does not include the term.Comment: 3 pages. Lattice2001(improvement
Progress towards a lattice determination of (moments of) nucleon structure functions
Using unimproved and non-perturbatively O(a) improved Wilson fermions,
results are given for the three lowest moments of unpolarised nucleon structure
functions. Renormalisation, chiral extrapolation and the continuum limit of the
matrix elements are briefly discussed. The simulations are performed for both
quenched and two flavours of unquenched fermions. No obvious sign of deviation
from linearity in the chiral extrapolations are found. (This is most clearly
seen in our quenched unimproved data, which extends to lighter quark mass.)
Possible quenching effects also seem to be small. The lowest moment thus
remains too large, so it seems to be necessary to reach smaller quark masses in
numerical simulations.Comment: 3 pages, Latex, 4 figures, Talk presented at
Lattice2001(matrixelement
Non-perturbative renormalisation and improvement of the local vector current for quenched and unquenched Wilson fermions
By considering the local vector current between nucleon states and imposing
charge conservation, we determine its renormalisation constant and quark mass
improvement coefficient for Symanzik improved Wilson fermions. The
computation is first performed for quenched fermions (and for completeness also
with unimproved fermions) and compared against known results. The two-flavour
unquenched case is then considered.Comment: 15 pages, 5 figures, Latex, Final versio
Perturbative Renormalization of Improved Lattice Operators
We derive bases of improved operators for all bilinear quark currents up to
spin two (including the operators measuring the first moment of DIS Structure
Functions), and compute their one-loop renormalization constants for arbitrary
coefficients of the improvement terms. We have thus control over O(a)
corrections, and for a suitable choice of improvement coefficients we are only
left with errors of O(a^2).Comment: 4 pages, LaTeX + 1 eps file + epscrc2.sty (included). Talk given to
the Lattice 97 International Symposium, 22-26 July 1997, Edinburgh, UK. Minor
changes in notatio
Lattice hadron matrix elements with the Schroedinger functional: the case of the first moment of non-singlet quark density
We present the results of a non-perturbative determination of the pion matrix
element of the twist-2 operator corresponding to the average momentum of
non-singlet quark densities. The calculation is made within the Schroedinger
functional scheme. We report the results of simulations done with the standard
Wilson action and with the non-perturbatively improved clover action and we
show that their ratio correctly extrapolates, in the continuum limit, to a
value compatible with the residual correction factor expected from perturbation
theory.Comment: LaTeX, 10 pages, 5 figure
Moments of Structure Functions in Full QCD
Moments of the quark density distribution, moments of the quark helicity
distribution, and the tensor charge are calculated in full QCD. Calculations of
matrix elements of operators from the operator product expansion have been
performed on lattices for Wilson fermions at
using configurations from the SESAM collaboration and at using
configurations from SCRI. One-loop perturbative renormalization corrections are
included. Selected results are compared with corresponding quenched
calculations and with calculations using cooled configurations.Comment: Lattice 2000 (Hadronic Matrix Elements), 4 pages, 5 figure
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