413,817 research outputs found
Improvement of the Staggered Fermion Operators
We present a complete and detailed derivation of the finite lattice spacing
corrections to staggered fermion matrix elements. Expanding upon arguments of
Sharpe, we explicitly implement the Symanzik improvement program demonstrating
the absence of order terms in the Symanzik improved action. We propose a
general program to improve fermion operators to remove corrections from
their matrix elements, and demonstrate this program for the examples of matrix
elements of fermion bilinears and . We find the former does have
corrections while the latter does not.Comment: 16 pages, latex, 1 figur
Perturbative Corrections for Staggered Four-Fermion Operators
We present results for one-loop matching coefficients between continuum
four-fermion operators, defined in the Naive Dimensional Regularization scheme,
and staggered fermion operators of various types. We calculate diagrams
involving gluon exchange between quark lines, and ``penguin'' diagrams
containing quark loops. For the former we use Landau gauge operators, with and
without improvement, and including the tadpole improvement suggested by
Lepage and Mackenzie.For the latter we use gauge-invariant operators. Combined
with existing results for two-loop anomalous dimension matrices and one-loop
matching coefficients, our results allow a lattice calculation of the
amplitudes for mixing and decays with all corrections of
included. We also discuss the mixing of operators with
lower dimension operators, and show that, with staggered fermions, only a
single lower dimension operator need be removed by non-perturbative
subtraction.Comment: 44 pages latex (uses psfig), 3 ps figures, all bundled using uufiles
(correctly this time!), UW/PT-93-
Non-perturbative improvement and renormalization of lattice operators
The Alpha Collaboration has proposed an optimal value for c_SW in the
Sheikholeslami-Wohlert action, chosen to remove O(a) effects. To measure
hadronic matrix elements to the same accuracy we need a method of finding O(a)
improved operators, and their renormalization constants. We determine the Z
factors by a non-perturbative method, measuring the matrix elements for single
quark states propagating through gauge fields in the Landau gauge. The data
show large effects coming from chiral symmetry breaking. This allows us to find
the improvement coefficients too, by requiring that the amount of chiral
symmetry breaking agrees with that predicted by the chiral Ward identities.Comment: 3 pages, Latex, 2 figures, epsf.sty and espcrc2.sty needed. Talk
given at Lattice9
Decomposition of nonlocal light-cone operators into harmonic operators of definite twist
Bilocal light-ray operators which are Lorentz scalars, vectors or
antisymmetric tensors, and which appear in various hard scattering QCD
processes, are decomposed into operators of definite twist. These operators are
harmonic tensor functions and their Taylor expansion consists of (traceless)
local light-cone operators with span irreducible representations of the Lorentz
group with definite spin j and common geometric twist (= dimension - spin).
Some applications concerning the nonforward matrix elements of these operators
and the generalization fo conformal light-cone operators of definite twist is
considered. The group theoretical background of the method has been made clear.Comment: 38 pages, AMSTEX Improvement of expressions for twist-3 and twist-4
tensor operators. to appear in Nucl. Phys.
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