227 research outputs found
Continuous external momenta in non-perturbative lattice simulations: a computation of renormalization factors
We discuss the usage of continuous external momenta for computing
renormalization factors as needed to renormalize operator matrix elements.
These kind of external momenta are encoded in special boundary conditions for
the fermion fields. The method allows to compute certain renormalization
factors on the lattice that would have been very difficult, if not impossible,
to compute with standard methods. As a result we give the renormalization group
invariant step scaling function for a twist-2 operator corresponding to the
average momentum of non-singlet quark densities.Comment: 28 pages, 10 figure
How the PHMC algorithm samples configuration space
We show that in practical simulations of lattice QCD with two dynamical light
fermion species the PHMC algorithm samples configuration space differently from
the commonly used HMC algorithm.Comment: 3 pages, 2 figures, LATTICE98 (Algorithms
Perturbative calculation of improvement coefficients to O(g^2a) for bilinear quark operators in lattice QCD
We calculate the O(g^2 a) mixing coefficients of bilinear quark operators in
lattice QCD using a standard perturbative evaluation of on-shell Green's
functions. Our results for the plaquette gluon action are in agreement with
those previously obtained with the Schr\"odinger functional method. The
coefficients are also calculated for a class of improved gluon actions having
six-link terms.Comment: 14 pages, REVTe
Non-perturbative renormalization of quark mass in Nf=2+1 QCD with the Schroedinger functional scheme
We present an evaluation of the quark mass renormalization factor for Nf=2+1
QCD. The Schroedinger functional scheme is employed as the intermediate scheme
to carry out non-perturbative running from the low energy region, where
renormalization of bare mass is performed on the lattice, to deep in the high
energy perturbative region, where the conversion to the renormalization group
invariant mass or the MS-bar scheme is safely carried out. For numerical
simulations we adopted the Iwasaki gauge action and non-perturbatively improved
Wilson fermion action with the clover term. Seven renormalization scales are
used to cover from low to high energy regions and three lattice spacings to
take the continuum limit at each scale. The regularization independent step
scaling function of the quark mass for the Nf=2+1 QCD is obtained in the
continuum limit. Renormalization factors for the pseudo scalar density and the
axial vector current are also evaluated for the same action and the bare
couplings as two recent large scale Nf=2+1 simulations; previous work of the
CP-PACS/JLQCD collaboration, which covered the up-down quark mass range heavier
than MeV and that of PACS-CS collaboration for much lighter
quark masses down to MeV. The quark mass renormalization factor is
used to renormalize bare PCAC masses in these simulations.Comment: 26 pages, 17 Postscript figures. Two tables are update
Pion parton distribution functions from lattice QCD
We report on recent results for the pion matrix element of the twist-2
operator corresponding to the average momentum of non-singlet quark densities.
For the first time finite volume effects of this matrix element are
investigated and come out to be surprisingly large. We use standard Wilson and
non-perturbatively improved clover actions in order to control better the
extrapolation to the continuum limit. Moreover, we compute, fully
non-perturbatively, the renormalization group invariant matrix element, which
allows a comparison with experimental results in a broad range of energy
scales. Finally, we discuss the remaining uncertainties, the extrapolation to
the chiral limit and the quenched approximation.Comment: Lattice2003(matrix), 3 pages, 4 figure
Recent Developments in Fermion Simulation Algorithms
A summary of recent developments in the field of simulation algorithms for
dynamical fermions is given.Comment: Plenary talk given at the International Symposium on Lattice Field
Theory, 4-8 June 1996, St. Louis, Mo, USA, Latex, 3 Figures, 7 page
Order a improved renormalization constants
We present non-perturbative results for the constants needed for on-shell
improvement of bilinear operators composed of Wilson fermions. We work
at and 6.2 in the quenched approximation. The calculation is done
by imposing axial and vector Ward identities on correlators similar to those
used in standard hadron mass calculations. A crucial feature of the calculation
is the use of non-degenerate quarks. We also obtain results for the constants
needed for off-shell improvement of bilinears, and for the scale and
scheme independent renormalization constants, (Z_A), (Z_V) and (Z_S/Z_P).
Several of the constants are determined using a variety of different Ward
identities, and we compare their relative efficacies. In this way, we find a
method for calculating that gives smaller errors than that used
previously. Wherever possible, we compare our results with those of the ALPHA
collaboration (who use the Schr\"odinger functional) and with 1-loop
tadpole-improved perturbation theory.Comment: 48 pages. Modified "axis" source for figures also included. Typos
corrected (version published in Phys. Rev. D
One-loop renormalization of heavy-light currents
We calculate the mass dependent renormalization factors of heavy-light
bilinears at one-loop order of perturbation theory, when the heavy quark is
treated with the Fermilab formalism.
We present numerical results for the Wilson and Sheikholeslami-Wohlert
actions, with and without tree-level rotation.
We find that in both cases our results smoothly interpolate from the static
limit to the massless limit.
We also calculate the mass dependent Brodsky-Lepage-Mackenzie scale ,
with and without tadpole-improvement.Comment: Lattice2001(improvement), 3 pages, 4 figure
Parton Distribution Functions with Twisted Mass Fermions
We present a first Wilson twisted mass fermion calculation of the matrix
element between pion states of the twist-2 operator, which is related to the
the lowest moment of the valence quark parton distribution function in a
pion. Using Wilson twisted mass fermions in the quenched approximation we
demonstrate that can be computed at small pseudoscalar meson masses down
to values of order 250 MeV. We investigate the scaling behaviour of this
physically important quantity by applying two definitions of the critical mass
and observe a scaling compatible with the expected O(a^2) behaviour in both
cases. A combined continuum extrapolation allows to obtain reliable results for
at very small pseudoscalar meson masses, which previously could not be
explored by lattice QCD simulations.Comment: 15 pages, 3 figure
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