5,175 research outputs found
Towards the continuum limit with quenched staggered quarks
We extend previous work on finite-size effects with dynamical staggered
quarks to the quenched approximation. We again emphasize the large volume limit
that is of interest for spectrum calculations which may hope to approach the
experimental values. Relying on new calculations at and recent work
with weaker couplings, we extrapolate to the continuum limit and find a nucleon
to rho mass ratio in close agreement with the experimental value and the value
obtained by extrapolations from calculations with Wilson quarks. Additional
calculations that should be done to improve the reliability of the
extrapolation are discussed.Comment: 3 pages, PostScript, Contribution to Lattice '9
Consistent Calculation of the Nucleon Electromagnetic Polarizabilities in Chiral Perturbation Theory Beyond Next-to-Leading Order
We calculate the nucleons' electromagnetic polarizabilities in heavy baryon
chiral perturbation theory including all terms to order . The
chiral prediction of the electric polarizabilities for the neutron and the
proton are in good agreement with the data. In the case of the magnetic
polarizabilities the big positive contribution from the
resonance is largely cancelled by a non--analytic loop contribution of the type. This novel effect helps to understand the rather small empirical
value of the nucleons' magnetic polarizability.Comment: 10 pp, TeX, BUTP-93/22 and CRN-93-3
Quenched staggered light hadron spectroscopy from at
We report our light hadron mass calculation based on an increased statistics
of 250 quenched gauge configurations on a (48^3 \times 64) lattice at (\beta =
6.5). Quark propagators are calculated for each of these configurations with
staggered wall source and point sink at quark mass values of (m_q = 0.01,
0.005, 0.0025) and (0.00125). We also did additional calculations to improve
our understanding of systematic biases arising from autocorrelation, source
size, and propagator calculations. Our earlier conclusions that the flavor
symmetry breaking is reduced and the ratio (m_N/m_\rho (\sim 1.25(4))) is small
remains robust.Comment: 3 pages and 4 figures, poster presented at the lattice 97 conferenc
The off-Shell Electromagnetic Vertex of the Nucleon in Chiral Perturbation Theory
We study the electromagnetic vertex of a nucleon in next-to-leading order
chiral perturbation theory (CPT). We consider the case where one of the
nucleons at the NN vertex is off its mass shell. We define relevant
measures for the off-shell dependence in the limited kinematical range allowed,
and analyze their expansion in the pion mass. The leading nonanalytic
contributions are calculated to estimate their size.Comment: 12 pages (LaTeX), 1 figure (available upon request), NIKHEF 93-P
Light hadron spectrum---MILC results with the Kogut-Susskind and Wilson actions
We present the current status of our ongoing calculations of the light hadron
spectrum with both Kogut-Susskind (KS) and Wilson quarks in the valence or
quenched approximation. We discuss KS quarks first and find that the chiral
extrapolation is potentially the biggest source of systematic error. For the
Wilson case, we focus on finite volume and source size effects at 6/g^2=5.7. We
find no evidence to support the claim that there is a finite volume effect
between N_s=16 and 24 of approximately 5%.Comment: 11 pages, 11 figures, LaTeX, uses espcrs2, epsf, Invited talk
presented by S. Gottlieb at Lattice QCD on Parallel Computers, University of
Tsukuba, March, 1997, to appear in the proceeding
Quenched Chiral Perturbation Theory for Baryons
We develop quenched chiral perturbation theory for baryons using the
graded-symmetry formalism of Bernard and Golterman and calculate non-analytic
contributions to the baryon masses coming from quenched chiral loops. The usual
term proportional to is substantially altered due to the
cancellation of diagrams with internal quark loops. In addition, the
``hairpin'' vertex leads to a new correction, proportional to . We
compare our results to numerical lattice data and use them to estimate the size
of the quenching error in the octet baryon masses.Comment: 7 pages (An abridged version of this note will appear in the
proceedings of Lattice'93. Latex + 14 postscript files, bundled using
uufiles. Needs psfig.) UW/PT-93-0
QCD Spectrum --- 1996
Progress on the calculation of the spectrum from lattice calculations is
reviewed. Particular emphasis is placed on discussing our ability to control
possible systematic errors coming from finite volume, and extrapolations in
quark mass and lattice spacing. Recent approaches based on improved actions are
compared.Comment: Plenary talk presented at LATTICE96(spectrum), 13 pages, LaTeX, 17
eps figures. Uses espcrc2, epsf. Additional figures may be found at:
http://physics.indiana.edu/~sg/lat96_spectrum.htm
Hadron Masses from the Valence Approximation to Lattice QCD
We evaluate pseudoscalar, vector, spin 1/2 and spin 3/2 baryon masses
predicted by lattice QCD with Wilson quarks in the valence (quenched)
approximation for a range of different values of lattice spacing, lattice
volume and quark mass. Extrapolating these results to physical quark mass, then
to zero lattice spacing and infinite volume we obtain values for eight mass
ratios. We also determine the zero lattice spacing, infinite volume limit of an
alternate set of five quantities found without extrapolation in quark mass.
Both sets of predictions differ from the corresponding observed values by
amounts consistent with the predicted quantities' statistical uncertainties.Comment: 108 pages of Latex, including 50 PostScript figures, tarred,
compressed and uuencoded. IBM-HET-94-3. (The first version of this posting
exceeded the size limit. I squeezed the second version in by dropping out the
figues. This version gets the figures in but has to be run through Latex and
dvips.
Hadron spectroscopy from lattice QCD
I present recent developments in the lattice QCD calculations of the light
hadron spectrum. Emphasis is placed on the limitation of the quenched
approximation in reproducing the observed spectrum and indications that the
discrepancy is reduced by introducing two flavors of light dynamical quarks.Comment: Talk presented at KEK-Tanashi symposium on "Physics of Hadrons and
Nuclei", 14-17 Dec. 1998, Tokyo, Japan. To be published in Nucl. Phys. A. 8
pages, 10 figure
Recent Results from the CP-PACS Collaboration
We present an overview of recent results from the CP-PACS computer on the
quenched light hadron spectrum and an on-going two-flavour full QCD study. We
find that our quenched hadron mass results are compatible with the mass
formulae predicted by quenched chiral perturbation theory, which we adopt in
our final analysis. Quenched hadron masses in the continuum limit show
unambiguous and systematic deviations from experiment. For our two-flavour full
QCD simulation we present preliminary results on the light hadron spectrum,
quark masses and the static potential. The question of dynamical sea quark
effects in these quantities is discussed.Comment: LATTICE98, plenary talk, LaTeX(espcrc2.sty), 13 pages, 23 figure
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