967 research outputs found
Approach to the Continuum Limit of the Quenched Hermitian Wilson-Dirac Operator
We investigate the approach to the continuum limit of the spectrum of the
Hermitian Wilson-Dirac operator in the supercritical mass region for pure gauge
SU(2) and SU(3) backgrounds. For this we study the spectral flow of the
Hermitian Wilson-Dirac operator in the range . We find that the
spectrum has a gap for and that the spectral density at zero,
, is non-zero for . We find that and, for
(exponential in the lattice spacing) as one goes to
the continuum limit. We also compute the topological susceptibility and the
size distribution of the zero modes. The topological susceptibility scales well
in the lattice spacing for both SU(2) and SU(3). The size distribution of the
zero modes does not appear to show a peak at a physical scale.Comment: 19 pages revtex with 9 postscript figures included by eps
Are Topological Charge Fluctuations in QCD Instanton Dominated?
We consider a recent proposal by Horv\'ath {\em et al.} to address the
question whether topological charge fluctuations in QCD are instanton dominated
via the response of fermions using lattice fermions with exact chiral symmetry,
the overlap fermions. Considering several volumes and lattice spacings we find
strong evidence for chirality of a finite density of low-lying eigenvectors of
the overlap-Dirac operator in the regions where these modes are peaked. This
result suggests instanton dominance of topological charge fluctuations in
quenched QCD.Comment: LaTeX, 15 pages, 8 postscript figures, minor improvements, version to
appear in PR
Non-Reversibility of Molecular Dynamics Trajectories
We study the non-reversibility of molecular dynamics trajectories arising
from the amplification of rounding errors. We analyse the causes of such
behaviour and give arguments, indicating that this does not pose a significant
problem for Hybrid Monte Carlo computations. We present data for pure SU(3)
gauge theory and for QCD with dynamical fermions on small lattices to
illustrate and to support some of our ideas.Comment: 3 pages LATEX, 4 color figures included using epsf. Talk presented at
LATTICE96(algorithms
Nucleon Structure from Lattice QCD
Recent advances in lattice field theory, in computer technology and in chiral
perturbation theory have enabled lattice QCD to emerge as a powerful
quantitative tool in understanding hadron structure. I describe recent progress
in the computation of the nucleon form factors and moments of parton
distribution functions, before proceeding to describe lattice studies of the
Generalized Parton Distributions (GPDs). In particular, I show how lattice
studies of GPDs contribute to building a three-dimensional picture of the
proton. I conclude by describing the prospects for studying the structure of
resonances from lattice QCD.Comment: 6 pages, invited plenary talk at NSTAR 2007, 5-8 September 2007,
Bonn, German
Spectroscopy using the Anisotropic Clover Action
The calculation of the light-hadron spectrum in the quenched approximation to
QCD using an anisotropic clover fermion action is presented. The tuning of the
parameters of the action is discussed, using the pion and rho dispersion
relation. The adoption of an anisotropic lattice provides clear advantages in
the determination of the baryonic resonances, and in particular that of the
so-called Roper resonance, the lightest radial excitation of the nucleon.Comment: Lattice2002(spectrum), 3 pages, 3 figures, to appear in Proceedings
of Lattice 200
Chiral Condensate in the Deconfined Phase of Quenched Gauge Theories
We compute the low lying spectrum of the overlap Dirac operator in the
deconfined phase of finite-temperature quenched gauge theory. It suggests the
existence of a chiral condensate which we confirm with a direct stochastic
estimate. We show that the part of the spectrum responsible for the chiral
condensate can be understood as arising from a dilute gas of instantons and
anti-instantons.Comment: Revtex, 16 pages, 3 postscript figure
Chiral properties of domain-wall fermions from eigenvalues of 4 dimensional Wilson-Dirac operator
We investigate chiral properties of the domain-wall fermion (DWF) system by
using the four-dimensional hermitian Wilson-Dirac operator. We first derive a
formula which connects a chiral symmetry breaking term in the five dimensional
DWF Ward-Takahashi identity with the four dimensional Wilson-Dirac operator,
and simplify the formula in terms of only the eigenvalues of the operator,
using an ansatz for the form of the eigenvectors. For a given distribution of
the eigenvalues, we then discuss the behavior of the chiral symmetry breaking
term as a function of the fifth dimensional length. We finally argue the chiral
property of the DWF formulation in the limit of the infinite fifth dimensional
length, in connection with spectra of the hermitian Wilson-Dirac operator in
the infinite volume limit as well as in the finite volume.Comment: Added a reference and modified the acknowledgmen
A Comparison of Clover and Wilson Spectroscopy in the Presence of Dynamical Quarks
We present preliminary results of light hadron spectroscopy using valence,
tadpole-improved, Clover fermions on an ensemble of gauge configurations
generated with 2 flavors of staggered fermions at a beta of 5.6. We compare the
slope and intercept of the curve M_V vs. M_PS^2 for Clover and Wilson fermions.
We show that a higher order chiral perturbation theory ansatz works very well
for chiral extrapolations.Comment: 4 pages latex with 4 Postscript figures, to be published in the
Proceedings of Lattice 9
Another determination of the quark condensate from an overlap action
I use the technique of Hernandez, et al (hep-lat/0106011) to convert a recent
calculation of the lattice-regulated quark condensate from an overlap action to
a continuum-regulated number. I find Sigma(MSbar)(mu = 2 GeV) = (282(6)
MeV)-cubed times (a-inverse/1766 MeV)-cubed from a calculation with the Wilson
gauge action at beta=5.9.Comment: 3 pages, Revtex, 1 postscript figure. References added. COLO-HEP-47
Schroedinger functional formalism with domain-wall fermion
Finite volume renormalization scheme is one of the most fascinating scheme
for non-perturbative renormalization on lattice.
By using the step scaling function one can follow running of renormalized
quantities with reasonable cost.
It has been established the Schroedinger functional is very convenient to
define a field theory in a finite volume for the renormalization scheme.
The Schroedinger functional, which is characterized by a
Dirichlet boundary condition in temporal direction, is well defined and works
well for the Yang-Mills theory and QCD with the Wilson fermion.
However one easily runs into difficulties if one sets the same sort of the
Dirichlet boundary condition for the overlap Dirac operator or the domain-wall
fermion.
In this paper we propose an orbifolding projection procedure to impose the
Schroedinger functional Dirichlet boundary condition on the domain-wall
fermion.Comment: 32 page
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