367 research outputs found
N* Masses from an Anisotropic Lattice QCD Action
We report N* masses in the spin 3/2 sector from a highly-improved anisotropic
action. States with both positive and negative parity are isolated via a parity
projection method. The extent to which spin projection is needed is examined.
The gross features of the splittings from the nucleon ground state show a trend
consistent with experimental results at the quark masses explored.Comment: Lattice2001(spectrum), 3 pages, 4 figures, new interpolating fiel
Baryon magnetic moments in the external field method
We present a calculation of the magnetic moments of the baryon octet and
decuplet using the external field method and standard Wilson gauge and fermion
actions in the quenched approximation. Progressively smaller static magnetic
fields are introduced on a latticeat beta=6.0 and the pion mass is
probed down to about 500 MeV. Magnetic moments are extracted from the linear
response of the masses to the external field.Comment: Lattice2004 (weak matrix elements), 3 pages, 8 figure
Baryon resonances from a novel fat-link fermion action
We present first results for masses of positive and negative parity excited
baryons in lattice QCD using an O(a^2) improved gluon action and a Fat Link
Irrelevant Clover (FLIC) fermion action in which only the irrelevant operators
are constructed with fat links. The results are in agreement with earlier
calculations of N^* resonances using improved actions and exhibit a clear mass
splitting between the nucleon and its chiral partner, even for the Wilson
fermion action. The results also indicate a splitting between the lowest J^P =
1/2^- states for the two standard nucleon interpolating fields.Comment: 5 pages, 3 figures, talk given by W.Melnitchouk at LHP 2001 workshop,
Cairns, Australi
Topological Charge Fluctuations and Low-Lying Dirac Eigenmodes
We discuss the utility of low-lying Dirac eigenmodes for studying the nature
of topological charge fluctuations in QCD. The implications of previous results
using the local chirality histogram method are discussed, and the new results
using the overlap Dirac operator in Wilson gauge backgrounds at lattice
spacings ranging from a~0.04 fm to a~0.12 fm are reported. While the degree of
local chirality does not change appreciably closer to the continuum limit, we
find that the size and density of local structures responsible for chiral
peaking do change significantly. The resulting values are in disagreement with
the assumptions of the Instanton Liquid Model. We conclude that the
fluctuations of topological charge in the QCD vacuum are not locally quantized.Comment: 3 pages, 4 figures, Lattice2001(confinement
Kaon Electromagnetic Production on Nuclei
The formation and excitation of hypernuclei through kaon photoproduction is
reviewed. Basic features of the production process are emphasized. The
possibility of extracting new information on hypernuclear structure and on the
wave function of the bound is discussed. New results are presented
for the quasifree production process . Observables of
this reaction are shown to be sensitive to the -nucleus final state
interaction.Comment: 10 pages, 4 figures. Invited talk given at the International
Conference on Hypernuclear and Strange Particle Physics (HYP97), Brookhaven
National Laboratory, USA, October 13-18, 1997. To be published in Nucl. Phys.
Magnetic polarizability of hadrons from lattice QCD
We extract the magnetic polarizability from the quadratic response of a
hadron's mass shift in progressively small static magnetic fields. The
calculation is done on a 24x12x12x24 lattice at a = 0.17 fm with an improved
gauge action and the clover quark action. The results are compared to those
from experiments and models where available.Comment: 3 pages, 3 figures, contribution to Lattice 2002 (spectrum
Overlap Fermions on a Lattice
We report results on hadron masses, fitting of the quenched chiral log, and
quark masses from Neuberger's overlap fermion on a quenched lattice with
lattice spacing fm. We used the improved gauge action which is shown
to lower the density of small eigenvalues for as compared to the Wilson
gauge action. This makes the calculation feasible on 64 nodes of CRAY-T3E. Also
presented is the pion mass on a small volume ( with a Wilson
gauge action at ). We find that for configurations that the
topological charge , the pion mass tends to a constant and for
configurations with trivial topology, it approaches zero possibly linearly with
the quark mass.Comment: Lattice 2000 (Chiral Fermion), 4 pages, 4 figure
Topological Charge Correlators, Spectral Bounds, and Contact Terms
The structure of topological charge fluctuations in the QCD vacuum is
strongly restricted by the spectral negativity of the Euclidean 2-point
correlator for and the presence of a positive contact term. Some
examples are considered which illustrate the physical origin of these
properties.Comment: Lattice 2002 Conference Proceeding
Spin-3/2 Nucleon and Delta Baryons in Lattice QCD
We present first results for masses of spin-3/2 N and Delta baryons in
lattice QCD using Fat-Link Irrelevant Clover (FLIC) fermions. Spin-3/2
interpolating fields providing overlap with both spin-3/2 and spin-1/2 states
are considered. In the isospin-1/2 sector, we observe, after appropriate spin
and parity projection, a strong signal for the J^P=3/2^- state together with a
weak but discernible signal for the 3/2^+ state with a mass splitting near that
observed experimentally. We also find good agreement between the 1/2^+/- masses
and earlier nucleon mass simulations with the standard spin-1/2 interpolating
field. For the isospin-3/2 Delta states, clear mass splittings are observed
between the various 1/2^+/- and 3/2^+/- channels, with the calculated level
orderings in good agreement with those observed empirically.Comment: 17 pages, 8 figures, 2 table
Multi-mass solvers for lattice QCD on GPUs
Graphical Processing Units (GPUs) are more and more frequently used for
lattice QCD calculations. Lattice studies often require computing the quark
propagators for several masses. These systems can be solved using multi-shift
inverters but these algorithms are memory intensive which limits the size of
the problem that can be solved using GPUs. In this paper, we show how to
efficiently use a memory-lean single-mass inverter to solve multi-mass
problems. We focus on the BiCGstab algorithm for Wilson fermions and show that
the single-mass inverter not only requires less memory but also outperforms the
multi-shift variant by a factor of two.Comment: 27 pages, 6 figures, 3 Table
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