93 research outputs found
Light Quenched Hadron Spectrum and Decay Constants on different Lattices
We present a study of (quenched) lattice configurations from
the APE collaboration, for using both the Wilson and the
SW-Clover fermion action. We determine the light hadronic spectrum and meson
decay constants. We extract the inverse lattice spacing using data at the
simulated values of the quark mass. We find an agreement with the experimental
data of for mesonic masses and for baryonic masses and
pseudoscalar decay constants. A larger deviation is present for the vector
decay constants.Comment: 3 pages, Talk presented at LATTICE96(spectrum
Hysteretic optimization for the Sherrington-Kirkpatrick spin glass
Hysteretic optimization is a heuristic optimization method based on the
observation that magnetic samples are driven into a low energy state when
demagnetized by an oscillating magnetic field of decreasing amplitude. We show
that hysteretic optimization is very good for finding ground states of
Sherrington-Kirkpatrick spin glass systems. With this method it is possible to
get good statistics for ground state energies for large samples of systems
consisting of up to about 2000 spins. The way we estimate error rates may be
useful for some other optimization methods as well. Our results show that both
the average and the width of the ground state energy distribution converges
faster with increasing size than expected from earlier studies.Comment: Physica A, accepte
Decay Constants of Heavy-Light Mesons
The decay constants of the heavy-light pseudoscalar mesons are studied in a
high statistics run using the Wilson action at and , and
the clover action at . The systematics of discretisation
errors are discussed. Our best estimates of the decay constants are: =
218(9) MeV, = 1.11(1) and we obtain preliminary values for .Comment: at the Dallas Lattice Conference, October 1993. 3 pages in a single
postscript file, uuencoded form. Rome Preprint 93/98
Pion-Nucleon Sigma Term in Lattice QCD
We calculate both connected and disconnected contribution to the -
-term in quenched lattice QCD with Wilson quark action on a lattice at . The latter is evaluated with the aid of the variant
wall source method, which was previously applied successfully for extraction of
- scattering lengths and meson mass. We found that the
disconnected contribution is about twice larger than the connected one. The
value for the full - term MeV is consistent
with the experimental estimates. The nucleon matrix element of the strange
quark density is fairly large in our result.Comment: 11 pages. Latex file. Figures are also included as ps file
Quenched -parameter with the Wilson and Clover actions at
We present results for the Kaon parameter from a sample of
configurations using the Wilson action and configurations using the
Clover action, on a lattice at . A slight
improvement of the chiral behaviour of is observed due to the Clover
action. We have also compared the results for obtained from two different
procedures for the boosting of the coupling constant . We observe a strong
dependence of on the prescription adopted for in the Wilson case,
contrary to the results of the Clover case which are almost unaffected by the
choice of . Combining some recently obtained non perturbative estimates for
the renormalisation constants with our Clover matrix element, we observe a
significant improvement in the chiral behaviour of .Comment: 3 pages, Latex, Postscript file with figures available at
ftp://hpteo.roma1.infn.it/pub/preprints/lat94/donini ; to appear in Lattice
'94, Nucl. Phys. (Proc.Suppl.
Light Quark Masses from Lattice QCD
We present estimates of the masses of light quarks using lattice data. Our
main results are based on a global analysis of all the published data for
Wilson, Sheikholeslami-Wohlert (clover), and staggered fermions, both in the
quenched approximation and with dynamical flavors. We find that the
values of masses with the various formulations agree after extrapolation to the
continuum limit for the theory. Our best estimates, in the MSbar scheme
at , are \mbar=3.4 +- 0.4 +- 0.3 MeV and in the quenched approximation. The results, \mbar = 2.7 +- 0.3 +-
0.3 MeV and , are preliminary. (A linear
extrapolation in would further reduce these estimates for the physical
case of three dynamical flavors.) These estimates are smaller than
phenomenological estimates based on sum rules, but maintain the ratios
predicted by chiral perturbation theory. The new results have a significant
impact on the extraction of from the Standard Model. Using
the same lattice data we estimate the quark condensate using the
Gell-Mann-Oakes-Renner relation. Again the three formulations give consistent
results after extrapolation to , and the value turns out to be
correspondingly larger, roughly preserving m_s \vev{\bar \psi \psi}.Comment: 32 pages. Package submitted in uufiles format: unpack and tex
paper.tex. Modified "axis" source for figures also included. Latex2e
document. Uncomment hyperref if available. This is the final published
versio
Progress and status of APEmille
We report on the progress and status of the APEmille project: a SIMD parallel
computer with a peak performance in the TeraFlops range which is now in an
advanced development phase. We discuss the hardware and software architecture,
and present some performance estimates for Lattice Gauge Theory (LGT)
applications.Comment: Talk presented at LATTICE97, 3 pages, Late
Hadron Properties just before Deconfinement
We have investigated hadron screening masses, the chiral condensate, and the
pion decay constant close to the deconfinement phase transition in the confined
phase of QCD. The simulations were done in the quenched approximation, on a
lattice of size \mbox{}. We examined temperatures ranging from
0.75\tc up to 0.92\tc. We see no sign of a temperature dependence in the
chiral condensate or the meson properties, but some temperature dependence for
the nucleon screening mass is not excluded.Comment: Postscript file, uuencoded compresse
Chiral Corrections to Lattice Calculations of Charge Radii
Logarithmic divergences in pion and proton charge radii associated with
chiral loops are investigated to assess systematic uncertainties in current
lattice determinations of charge radii. The chiral corrections offer a possible
solution to the long standing problem of why present lattice calculations yield
proton and pion radii which are similar in size.Comment: PostScript file only. Ten pages. Figures included. U. of MD Preprint
#92-19
Recent Developments in Lattice QCD
I review the current status of lattice QCD results. I concentrate on new
analytical developments and on numerical results relevant to phenomenology.Comment: 35 pages, 4 figures (Figures are excerpted from others' work and are
not included) Uses harvmac.te
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