14,192 research outputs found
Constitutional Law - State Action - Closing Rather Than Desegregating Recreational Facilities. Palmer v. Thompson, 91 S. Ct. 1940 (1971)
The Sigma Commutator from Lattice QCD
As a direct source of information on chiral symmetry breaking within QCD, the
sigma commutator is of considerable importance. Since hadron structure is a
non-perturbative problem, numerical calculations on a space-time lattice are
currently the only rigorous approach. With recent advances in the calculation
of hadron masses within full QCD, it is of interest to see whether the sigma
commutator can be calculated directly from the dependence of the nucleon mass
on the input quark mass. We show that, provided the correct chiral behaviour of
QCD is respected in the extrapolation to realistic quark masses, one can indeed
obtain a fairly reliable determination of the sigma commutator using present
lattice data. For two-flavour dynamical fermion QCD the sigma commutator lies
between 45 and 55 MeV based on recent data from CP-PACS and UKQCD.Comment: 4 pages, 3 figures, uses espcrc1.sty and epsfig.sty. Contribution to
the proceedings of the International Conference on Quark Nuclear Physics held
in Adelaide Feb. 200
Chiral Corrections to Baryon Masses Calculated within Lattice QCD
Consideration of the analytic properties of pion-induced baryon self energies
leads to new functional forms for the extrapolation of light baryon masses.
These functional forms reproduce the leading non-analytic behavior of chiral
perturbation theory, the correct non-analytic behavior at the threshold
and the appropriate heavy-quark limit. They involve only three unknown
parameters, which may be obtained by fitting lattice QCD data. Recent dynamical
fermion results from CP-PACS and UKQCD are extrapolated using these new
functional forms. We also use these functions to probe the limit of
applicability of chiral perturbation theory.Comment: 4 pages, 2 figures, Contribution to the Proceedings of the 15th
Particles and Nuclei International Conference (PANIC 99), Uppsala, Sweden,
June 10-16, 199
Chiral Nonanalytic Behaviour: The Edinburgh Plot
The Edinburgh Plot is a scale independent way of presenting lattice QCD
calculations over a wide range of quark masses. In this sense it is appealing
as an indicator of how the approach to physical quark masses is progressing.
The difficulty remains that even the most state of the art calculations are
still at quark masses that are too heavy to apply dimensionally-regulated
chiral perturbation theory. We present a method allowing predictions of the
behaviour of the Edinburgh plot, in both the continuum, and on the lattice.Comment: 3 pages, 4 figures, Lattice2002(Spectrum
Baryon Mass Extrapolation
Consideration of the analytical properties of pion-induced baryon
self-energies leads to new functional forms for the extrapolation of light
baryon masses. These functional forms reproduce the leading non-analytic
behavior of chiral perturbation theory, the correct heavy-quark limit and have
the advantage of containing information on the extended structure of hadrons.
The forms involve only three unknown parameters which may be optimized by
fitting to present lattice data. Recent dynamical fermion results from CP-PACS
and UK-QCD are extrapolated using these new functional forms. We also use these
functions to probe the limit of the chiral perturbative regime and shed light
on the applicability of chiral perturbation theory to the extrapolation of
present lattice QCD results.Comment: LATTICE99 (QCD Spectrum and Quark Masses
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