75 research outputs found
Glueballs and string breaking from full QCD
We present results on the static potential, and torelon and glueball masses
from simulations of QCD with two flavours of dynamical Wilson fermions on
and lattices at .Comment: Talk presented by Gunnar Bali at International Symposium on Lattice
Field Theories (Lattice 97), Edinburgh, July 1997, 3 pages LaTeX
(epscrc2.sty) with 4 eps figure
SESAM and TXL Results for Wilson Action--A Status Report
Results from two studies of full QCD with two flavours of dynamical Wilson
fermions are presented. At beta=5.6, the region 0.83 > m_pi/m_rho > 0.56 at
m_pia > 0.23 L^{-1} is explored. The SESAM collaboration has generated
ensembles of about 200 statistically independent configurations on a 16^3 x
32-lattice at three different kappa-values and is entering the final phase of
data analysis. The TXL simulation on a 24^3 x 40-lattice at two kappa-values
has reached half statistics and data analysis has started recently, hence most
results presented here are preliminary. The focus of this report is fourfold:
we demonstrate that algorithmic improvements like fast Krylov solvers and
parallel preconditioning recently introduced can be put into practise in full
QCD simulations, we present encouraging observations as to the critical
dynamics of the Hybrid Monte Carlo algorithm in the approach to the chiral
limit, we mention signal improvements of noisy estimator techniques for
disconnected diagrams to the pi-N sigma term, and we report on SESAM's results
for light hadron spectrum, light quark masses, and heavy quarkonia.Comment: 24 pages, tex + postscript figures, to appear in Proceedings of Int.
Workshop "Lattice QCD on Parallel Computers", University of Tsukuba, Japa
Light Quark Physics with Dynamical Wilson Fermions
We present results for spectroscopy, quark masses and decay constants
obtained from SESAM's and TkL's large statistics simulations of QCD with two
dynamical Wilson fermions.Comment: 3 pages; to appear in the proceedings of Lat.'9
Light Quark Masses with Dynamical Wilson Fermions
We determine the masses of the light and the strange quarks in the
-scheme using our high-statistics lattice simulation of QCD with
dynamical Wilson fermions. For the light quark mass we find
, which is lower than in quenched
simulations. For the strange quark, in a sea of two dynamical light quarks, we
obtain .Comment: 10 pages (latex file, uses epsf-style
On Lattice QCD with Many Flavors
We discuss the confining and chiral-symmetry breaking properties of QCD with
a large number of flavors . In a Monte Carlo simulation of QCD with staggered fermions, we find clear evidence of a first order bulk phase
transition which separates phases with broken and unbroken chiral symmetry.
This is consistent with extrapolations of earlier studies with smaller ,
and is also as expected from general arguments. Thus, even when the
perturbative renormalization group flow has a new infrared stable fixed point
near the origin, lattice artifacts induce chiral symmetry breaking, and
presumably confinement, at sufficiently strong coupling.Comment: 10 pages, LaTeX, figures part of the LaTeX fil
Light and Strange Hadron Spectroscopy with Dynamical Wilson Fermions
We present the final analysis of the light and strange hadron spectra from a full QCD lattice simulation with two degenerate dynamical sea quark flavours at corresponding to the range are investigated. For reference we also ran a quenched simulation at , which is the point of equal lattice spacing, . In the light sector, we find the chiral extrapolation to physical u- and d- masses to present a major source of uncertainty, comparable to the expected size of unquenching effects. From linear and quadratic fits we can estimate the errors on the hadron masses made from light quarks to be on a 15 % level prior to the continuum extrapolation. For the hadrons with strange valence quark content, the approximation to QCD appears not to cure the well-known failure of quenched QCD to reproduce the physical splitting
String Breaking in Lattice Quantum Chromodynamics
The separation of a heavy quark and antiquark pair leads to the formation of
a tube of flux, or string, which should break in the presence of light
quark-antiquark pairs. This expected zero temperature phenomenon has proven
elusive in simulations of lattice QCD. We present simulation results that show
that the string does break in the confining phase at nonzero temperature.Comment: 11 pages RevTeX, including 4 encapsulated Postscript figures.
version2: minor corrections to reference
Scanning the Topological Sectors of the QCD Vacuum with Hybrid Monte Carlo
We address a long standing issue and determine the decorrelation efficiency
of the Hybrid Monte Carlo algorithm (HMC), for full QCD with Wilson fermions,
with respect to vacuum topology. On the basis of five state-of-the art QCD
vacuum field ensembles (with 3000 to 5000 trajectories each and
m_pi/m_rho-ratios in the regime >0.56, for two sea quark flavours) we are able
to establish, for the first time, that HMC provides sufficient tunneling
between the different topological sectors of QCD. This will have an important
bearing on the prospect to determine, by lattice techniques, the topological
susceptibility of the vacuum, and topology sensitive quantities like the spin
content of the proton, or the eta' mass.Comment: 5 pages, 4 eps-figure
Going chiral: overlap versus twisted mass fermions
We compare the behavior of overlap fermions, which are chirally invariant,
and of Wilson twisted mass fermions at full twist in the approach to the chiral
limit. Our quenched simulations reveal that with both formulations of lattice
fermions pion masses of O(250 MeV) can be reached in practical applications.
Our comparison is done at a fixed value of the lattice spacing a=0.123 fm. A
number of quantities are measured such as hadron masses, pseudoscalar decay
constants and quark masses obtained from Ward identities. We also determine the
axial vector renormalization constants in the case of overlap fermions.Comment: 22 pages, 10 figure
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