944 research outputs found
Effects of non-perturbatively improved dynamical fermions in UKQCD simulations
We present results for QCD with 2 degenerate flavours of quark using a
non-perturbatively improved action on a lattice volume of where
the bare gauge coupling and bare dynamical quark mass have been chosen to
maintain a fixed physical lattice spacing and volume (1.71 fm). By comparing
measurements from these matched ensembles, including quenched ones, we find
evidence of dynamical quark effects on the short distance static potential, the
scalar glueball mass and the topological susceptibility. There is little
evidence of effects on the light hadron spectrum over the range of quark masses
studied ().Comment: Lattice 2000 (Spectrum and quark masses), 4 pages, 5 figure
Strangeness-exchange interactions at high energies
In Chapter 1 we discuss the importance of a study of high energy strangeness-exchange reactions in elucidating the exchange mechanisms and symmetry properties of meson-baryon scattering. The cross-section and polarisation data for KN→πΣ, Δ and πKN→πΣ, Δ are reviewed in Chapter 2. An exchange-degenerate poles with weak cuts model for the data is proposed, and the resulting successful polarisation and unsuccessful cross-section descriptions are discussed. The model's failure to reproduce the well-known line reversal cross-section inequality at intermediate energies is interpreted in terms of low energy resonance effects. A unified treatment of non-zero exotic exchange processes and line reversal symmetry violation in terms of Regge-Regge cuts is presented in Chapter 3. After a theoretical appraisal of a multiple scattering approximation for these cuts we present explicit calculations of the exotic strangeness-exchange cross- sections for K(^-)p-π(^+)Σ(^-) and π(^-)p→K(^+)Σ(^-). It is shown that the small size of the data for these is not easily explained. Since we also show that the inclusion of non-leading cuts aggravates the disagreement between data and the leading cuts model, the usefulness of Regge-Regge cut descriptions at intermediate energies is called into question
Approximate actions for dynamical fermions
Recent developments and applications of approximate actions for full lattice
QCD are described. We present first results based on the stochastic estimation
of the fermion determinant on configurations at .Comment: 3 pages, Latex, no figures, Contribution to Lattice 97, The XV
International Symposium on Lattice Field Theory, Edinburgh 22-26 July 199
Unquenching the Schwinger Model (revised)
We study the quenched and unquenched lattice Schwinger model with Wilson
fermions. The lowest non-trivial order of the systematic expansion recently
proposed by Sexton and Weingarten is shown to allow good estimates of long
distance physics from quenched configurations. Results for the static potential
and the lowest bound state mass are presented.Comment: 4 pages, 2 figures, self-unpacking uuencoded compressed postscript
Contribution to Lattice 95 [Revision: value corrected on p.3
Scalar glueball and meson spectroscopy in unquenched lattice QCD with improved staggered quarks
We present results of an exploratory study of singlet scalar states in
unquenched QCD using both glueball and meson operators. Results for non-singlet
non-strange scalar mesons are also presented. We use Asqtad improved staggered
fermions and gauge configurations generated by the MILC collaboration at
lattice spacings of .12 and .09 fm. In this formulation, the glueball mass is
not significantly different from the quenched value at finite lattice spacing.
Significant taste violations are present in the scalar sector. At light quark
masses, decay channels complicate the mass determinations. There is some
evidence that the non-strange singlet meson lies below the non-singlet meson.Comment: Lattice 2005 (hadron spectrum and quark masses), 6 pages, 4 figure
Pseudoscalar singlet physics with staggered fermions
We report on progress in measuring disconnected correlators associated with
pseudoscalar flavor-singlet mesons. This will eventually allow us to compute
the masses of the eta and eta' mesons. Flavor-singlet physics also presents an
interesting test of the staggered fermion formulation, as disconnected
correlators are sensitive to whether the same action governs both sea quarks
and valence quarks. It can also help test the validity of the ``fourth-root
trick'' used in unquenched lattice calculations where the number of flavors
.Comment: Talk presented at Lattice 2005 (Hadron spectrum and quark masses), 6
pages, 3 figure
Glueball mass measurements from improved staggered fermion simulations
We present the first 2+1 flavour spectrum measurements of glueball states
using high statistics simulations with improved staggered fermions. We find a
spectrum consistent with quenched measurements of scalar, pseudoscalar
andtensor glueball states. The measurements were made using 5000 configurations
at a lattice spacing of 0.123 fm and pion mass of 280 MeV and 3000
configurations at 0.092 fm with a pion mass of 360 MeV. We see some evidence of
coupling to 2 pion states. We compare our results with the experimental
glueball candidate spectrum as well as quenched glueball estimates.Comment: 22 pages, 19 figures and 8 tables, minor additions on mixing
post-refere
Tuning Actions and Observables in Lattice QCD
We propose a strategy for conducting lattice QCD simulations at fixed volume
but variable quark mass so as to investigate the physical effects of dynamical
fermions. We present details of techniques which enable this to be carried out
effectively, namely the tuning in bare parameter space and efficient stochastic
estimation of the fermion determinant. Preliminary results and tests of the
method are presented. We discuss further possible applications of these
techniques.Comment: 17 pages, 4 eps figures; affiliation correction in this header +
minor post-referee addition
Parallel Tempering in Lattice QCD with O(a)-Improved Wilson Fermions
We present details of our investigation of the Parallel Tempering algorithm. We consider the application of action matching technology to the selection of parameters. We then present a simple model of the autocorrelations for a particular parallel tempered system. Finally we present numerical results from applying the algorithm to lattice QCD with O(a)-improved dynamical fermions with twin ensemble system
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