333 research outputs found
The glueball spectrum from an anisotropic lattice study
The spectrum of glueballs below 4 GeV in the SU(3) pure-gauge theory is
investigated using Monte Carlo simulations of gluons on several anisotropic
lattices with spatial grid separations ranging from 0.1 to 0.4 fm. Systematic
errors from discretization and finite volume are studied, and the continuum
spin quantum numbers are identified. Care is taken to distinguish single
glueball states from two-glueball and torelon-pair states. Our determination of
the spectrum significantly improves upon previous Wilson action calculations.Comment: 14 pages, 8 figures, uses REVTeX and epsf.sty (final version
published in Physical Review D
Nucleon, and excited states in lattice QCD
The energies of the excited states of the Nucleon, and are
computed in lattice QCD, using two light quarks and one strange quark on
anisotropic lattices. The calculation is performed at three values of the light
quark mass, corresponding to pion masses = 392(4), 438(3) and 521(3)
MeV. We employ the variational method with a large basis of interpolating
operators enabling six energies in each irreducible representation of the
lattice to be distinguished clearly. We compare our calculation with the
low-lying experimental spectrum, with which we find reasonable agreement in the
pattern of states. The need to include operators that couple to the expected
multi-hadron states in the spectrum is clearly identified.Comment: Revised for publication. References added, Table VI expanded to add
strange baryon multiparticle thresholds and multiparticle thresholds added to
Figs. 4, 5 and 6. 15 pages, 6 figure
Multi-hadron states in Lattice QCD spectroscopy
The ability to reliably measure the energy of an excited hadron in Lattice
QCD simulations hinges on the accurate determination of all lower-lying
energies in the same symmetry channel. These include not only single-particle
energies, but also the energies of multi-hadron states. This talk deals with
the determination of multi-hadron energies in Lattice QCD. The
group-theoretical derivation of lattice interpolating operators that couple
optimally to multi-hadron states is described. We briefly discuss recent
algorithmic developments which allow for the efficient implementation of these
operators in software, and present numerical results from the Hadron Spectrum
Collaboration.Comment: 5 pages, 3 figures, talk given at Hadron 2009, Tallahassee, Florida,
December 1, 200
Tadpole-improved SU(2) lattice gauge theory
A comprehensive analysis of tadpole-improved SU(2) lattice gauge theory is
made. Simulations are done on isotropic and anisotropic lattices, with and
without improvement. Two tadpole renormalization schemes are employed, one
using average plaquettes, the other using mean links in Landau gauge.
Simulations are done with spatial lattice spacings in the range of about
0.1--0.4 fm. Results are presented for the static quark potential, the
renormalized lattice anisotropy (where is the ``temporal''
lattice spacing), and for the scalar and tensor glueball masses. Tadpole
improvement significantly reduces discretization errors in the static quark
potential and in the scalar glueball mass, and results in very little
renormalization of the bare anisotropy that is input to the action. We also
find that tadpole improvement using mean links in Landau gauge results in
smaller discretization errors in the scalar glueball mass (as well as in the
static quark potential), compared to when average plaquettes are used. The
possibility is also raised that further improvement in the scalar glueball mass
may result when the coefficients of the operators which correct for
discretization errors in the action are computed beyond tree level.Comment: 14 pages, 7 figures (minor changes to overall scales in Fig.1; typos
removed from Eqs. (3),(4),(15); some rewording of Introduction
Chiral Suppression of Scalar Glueball Decay
Because glueballs are SU(3)_{Flavor} singlets, they are expected to couple
equally to u,d, and s quarks, so that equal coupling strengths to \pi^+\pi^-
and K^+K^- are predicted. However, we show that chiral symmetry implies the
scalar glueball amplitude for G_0 \to \qbq is proportional to the quark mass,
so that mixing with \sbs mesons is enhanced and decays to K^+K^- are favored
over \pi^+\pi^-. Together with evidence from lattice calculations and from
experiment, this supports the hypothesis that f_0(1710) is the ground state
scalar glueball.Comment: 9 pages; This revision reconciles posting (approximately) with
published version. Posting contains figures that are omitted in the
publicatio
Lattice study on kaon nucleon scattering length in the I=1 channel
Using the tadpole improved clover Wilson quark action on small, coarse and
anisotropic lattices, scattering length in the I=1 channel is calculated
within quenched approximation. The results are extrapolated towards the chiral
and physical kaon mass region. Finite volume and finite lattice spacing errors
are also analyzed and a result in the infinite volume and continuum limit is
obtained which is compatible with the experiment and the results from Chiral
Perturbation Theory.Comment: 15 pages, 4 figures, typeset by latex using elsart.cls,minor change
Scaling and Further Tests of Heavy Meson Decay Constant Determinations from Nonrelativistic QCD
We present results for the B_s meson decay constant f_{B_s} from simulations
at three lattice spacings in the range a^{-1}=1.1 to 2.6 GeV using NRQCD heavy
quarks and clover light quarks in the quenched approximation. We study scaling
of this quantity and check the consistency between mesons decaying from rest
and from a state with nonzero spatial momentum. The cancellation of power law
contributions that arise in the NRQCD formulation of heavy-light currents is
discussed. On the coarsest lattice the D_s meson decay constant f_{D_s} is
calculated. Our best values for the decay constants are given by f_{B_s} =
187(4)(4)(11)(2)(7)(6) MeV and f_{D_s} = 223(6)(31)(38)(23)(9)(^{+3}_{-1}) MeV.Comment: 29 pages with 7 postscript figures, improved error analysis, version
to appear in Physical Review
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