1,147 research outputs found
Topology conserving gauge action and the overlap-Dirac operator
We apply the topology conserving gauge action proposed by Luescher to the
four-dimensional lattice QCD simulation in the quenched approximation. With
this gauge action the topological charge is stabilized along the hybrid Monte
Carlo updates compared to the standard Wilson gauge action. The quark potential
and renormalized coupling constant are in good agreement with the results
obtained with the Wilson gauge action. We also investigate the low-lying
eigenvalue distribution of the hermitian Wilson-Dirac operator, which is
relevant for the construction of the overlap-Dirac operator.Comment: 27pages, 11figures, accepted versio
Lattice study of vacuum polarization function and determination of strong coupling constant
We calculate the vacuum polarization functions on the lattice using the
overlap fermion formulation.By matching the lattice data at large momentum
scales with the perturbative expansion supplemented by Operator Product
Expansion (OPE), we extract the strong coupling constant in
two-flavor QCD as =
GeV, where the errors are statistical and systematic, respectively. In
addition, from the analysis of the difference between the vector and
axial-vector channels, we obtain some of the four-quark condensates.Comment: 24 pages, 9 figures, enlarged version published in Phys. Rev.
A new scheme for the running coupling constant in gauge theories using Wilson loops
We propose a new renormalization scheme of the running coupling constant in
general gauge theories using the Wilson loops. The renormalized coupling
constant is obtained from the Creutz ratio in lattice simulations and the
corresponding perturbative coefficient at the leading order. The latter can be
calculated by adopting the zeta-function resummation techniques. We perform a
benchmark test of our scheme in quenched QCD with the plaquette gauge action.
The running of the coupling constant is determined by applying the step-scaling
procedure. Using several methods to improve the statistical accuracy, we show
that the running coupling constant can be determined in a wide range of energy
scales with relatively small number of gauge configurations.Comment: 30pages, figs and comments added,reference added(v3
B^0-\bar{B}^0 mixing with quenched lattice NRQCD
We present our recent results for the B-parameters, which parameterize the
\Delta B=2 transition amplitudes. Calculations are made in quenched QCD at
\beta=5.7, 5.9, and 6.1, using NRQCD for heavy quark and the -improved
action for light quark. The operators are perturbatively renormalized including
corrections of O(\alpha_s/am_Q). We examine scaling behavior of the
B-parameters in detail, and discuss the systematic uncertainties using scatter
of results with different analysis procedures adopted. As a result, we find
B_{B_d}(m_b)=0.84(2)(8), B_{B_s}/B_{B_d}=1.017(10)(^{+4}_{-0}) and
B_{S_s}(m_b)=0.87(1)(9)(^{+1}_{-0}) in the quenched approximation.Comment: Lattice 2000 (Heavy Quark Physics), 4 pages, 4 eps-figures, Latex,
typo correcte
Heavy quark expansion parameters from lattice NRQCD
Using the lattice NRQCD action for heavy quark, we calculate the heavy quark
expansion parameters and for heavy-light mesons and
heavy-light-light baryons. The results are compared with the mass differences
among heavy hadrons to test the validity of HQET relations on the lattice.Comment: Lattice2001(heavyquark), 3 pages, 4 figure
Exploration of sea quark effects in two-flavor QCD with the O(a)-improved Wilson quark action
We explore sea quark effects in the light hadron mass spectrum in a
simulation of two-flavor QCD using the nonperturbatively O(a)-improved Wilson
fermion action. In order to identify finite-size effects, light meson masses
are measured on 12^3x48, 16^3x48 and 20^3x48 lattices with a~0.1 fm. On the
largest lattice, where the finite-size effect is negligible, we find a
significant increase of the strange vector meson mass compared to the quenched
approximation. We also investigate the quark mass dependence of pseudoscalar
meson masses and decay constants and test the consistency with (partially
quenched) chiral perturbation theory.Comment: 3 pages, 3 figures, Lattice2001(spectrum
An exact algorithm for three-flavor QCD with -improved Wilson fermions
We present an exact dynamical QCD simulation algorithm for the
-improved Wilson fermion with odd number of flavors. Our algorithm is an
extension of the non-Hermitian polynomials HMC algorithm proposed by Takaishi
and de Forcrand previously. In our algorithm, the systematic errors caused by
the polynomial approximation of the inverse of Dirac operator is removed by a
noisy-Metropolis test. For one flavor quark it is achieved by taking the square
root of the correction matrix explicitly. We test our algorithm for the case of
on a moderately large lattice size (). The
case is also investigated.Comment: Lattice 2001 (algorithm), 3 pages, LaTeX2e with espcrc2.st
Two-dimensional Superfluidity and Localization in the Hard-Core Boson Model: a Quantum Monte Carlo Study
Quantum Monte Carlo simulations are used to investigate the two-dimensional
superfluid properties of the hard-core boson model, which show a strong
dependence on particle density and disorder. We obtain further evidence that a
half-filled clean system becomes superfluid via a finite temperature
Kosterlitz-Thouless transition. The relationship between low temperature
superfluid density and particle density is symmetric and appears parabolic
about the half filling point. Disorder appears to break the superfluid phase up
into two distinct localized states, depending on the particle density. We find
that these results strongly correlate with the results of several experiments
on high- superconductors.Comment: 10 pages, 3 figures upon request, RevTeX version 3, (accepted for
Phys. Rev. B
Non-trivial phase structure of QCD with -improved Wilson fermion at zero temperature
JLQCD collaboration recently started the QCD simulations with the
-improved Wilson fermion action employing an exact fermion algorithm
developed for odd number of quark flavors. It is found that this theory has an
unexpected non-trivial phase structure in the plane even at
zero temperature. A detailed study is made to understand the nature of the
observed phase transitions and to find the way of avoiding untolerably large
lattice artifacts associated with the phase transition.Comment: 3 pages, 5 figures, Lattice2001(spectrum
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