188 research outputs found
A new approach for Delta form factors
We discuss a new approach to reducing excited state contributions from two-
and three-point correlation functions in lattice simulations. For the purposes
of this talk, we focus on the Delta(1232) resonance and discuss how this new
method reduces excited state contamination from two-point functions and mention
how this will be applied to three-point functions to extract hadronic form
factors.Comment: 4 pages, 3 figures, talk given at MENU 2010, Williambsurg, V
Extrapolation Methods for the Dirac Inverter in Hybrid Monte Carlo
In Hybrid Monte Carlo(HMC) simulations for full QCD, the gauge fields evolve
smoothly as a function of Molecular Dynamics (MD) time. Thus we investigate
improved methods of estimating the trial solutions to the Dirac propagator as
superpositions of the solutions in the recent past. So far our best
extrapolation method reduces the number of Conjugate Gradient iterations per
unit MD time by about a factor of 4. Further improvements should be forthcoming
as we further exploit the information of past trajectories.Comment: latex file with espcrc2 styl
Variants of fattening and flavor symmetry restoration
We study the effects of different "fat link" actions for Kogut-Susskind
quarks on flavor symmetry breaking. Our method is mostly empirical - we compute
the pion spectrum with different valence quark actions on common sets of sample
lattices. Different actions are compared, as best we can, at equivalent
physical points. We find significant reductions in flavor symmetry breaking
relative to the conventional or to the "link plus staple" actions, with a
reasonable cost in computer time. We also develop and test a scheme for
approximate unitarization of the fat links. While our tests have concentrated
on the valence quark action, our results will be useful in designing
simulations with dynamical quarks.Comment: 16 pages, LaTeX, PostScript figures include
Thermodynamics with 3 and 2+1 Flavors of Improved Staggered Quarks
We present preliminary results from exploring the phase diagram of finite
temperature QCD with three degenerate flavors and with two light flavors and
the mass of the third held approximately at the strange quark mass. We use an
order Symanzik improved gauge action and an order
improved staggered quark action. The improved staggered
action leads to a dispersion relation with diminished lattice artifacts, and
hence better thermodynamic properties. It decreases the flavor symmetry
breaking of staggered quarks substantially, and we estimate that at the
transition temperature for an to lattice {\em all} pions will
be lighter than the lightest kaon. Preliminary results on lattices with
, 6 and 8 are presented.Comment: 3 pages, 6 figures, contribution to Lattice2001(hightemp) August
19--24, 2001, Berlin, German
Calculation of the neutron electric dipole moment with two dynamical flavors of domain wall fermions
We present a study of the neutron electric dipole moment () within
the framework of lattice QCD with two flavors of dynamical lig ht quarks. The
dipole moment is sensitive to the topological structure of the gaug e fields,
and accuracy can only be achieved by using dynamical, or sea quark, calc
ulations. However, the topological charge evolves slowly in these calculations,
le ading to a relatively large uncertainty in . It is shown, using
quenched configurations, that a better sampling of the charge d istribution
reduces this problem, but because the CP even part of the fermion determinant
is absent, both the topological charge dis tribution and are
pathological in the chiral limit. We discuss the statistical and systematic
uncertainties arising from the topological charge distr ibution and unphysical
size of the quark mass in our calculations and prospects fo r eliminating them.
Our calculations employ the RBC collaboration two flavor domain wall fermion
and DBW2 gauge action lattices with inverse lattice spacing 1.7
GeV, physical volume fm), and light quark mass roughly equal
to the strange quark mass ( and 0.04). We determine a value of
the electric dipole moment that is zero withi n (statistical) errors, e--fm at the smaller sea quark mass. Satisfactory
results for the magnetic and electric form factors of the proton and neutron
are also obtained and presented.Comment: 46 pages. Changed one author addres
Diquarks: a QCD sum rule perspective
We propose a phenomenological QCD sum rule with an explicit diquark field to
investigate the essential ingredients inside the hadrons. Introducing the mass
(m_\phi) and the condensate (\phi^2) for the diquark field as parameters in the
model, we find that the sum rule works well for Lambda, Lambda_c and Lambda_b.
This implies that these Lambda baryons can be represented by a diquark and a
quark configuration. We also find that there is a duality relation among the
parameters (m_\phi, \phi^2), for which the sum rule is equally good. In the
limit when \phi^2 =0 we find m_\phi=0.4 GeV, which can be thought as the
constituent diquark mass.Comment: 4 pages, 4 figures, revised version published in Phys. Rev.
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