428 research outputs found
Hadron spectroscopy and static quark potential in full QCD: A comparison of improved actions on the CP-PACS
We present first results from a full QCD calculation on the CP-PACS,
comparing various actions at and --0.9. We use the plaquette and a renormalization group improved action for
the gluons, and the Wilson and the SW-Clover action for quarks. We find that
significant improvements in the hadron spectrum results from improving the
quarks, while the gluon improvement is required for a rotationally invariant
static potential. An ongoing effort towards exploring the chiral limit in full
QCD is described.Comment: 6 pages, based on talks presented by R. Burkhalter and T. Kaneko at
Lattice97, Edinburg
Quenched Approximation Artifacts: A study in 2-dimensional QED
The spectral properties of the Wilson-Dirac operator in 2-dimensional QED
responsible for the appearance of exceptional configurations in quenched
simulations are studied in detail. The mass singularity structure of the
quenched functional integral is shown to be extremely compicated, with multiple
branch points and cuts. The connection of lattice topological charge and
exactly real eigenmodes is explored using cooling techniques. The lattice
volume and spacing dependence of these modes is studied, as is the effect of
clover improvement of the action. A recently proposed modified quenched
approximation is applied to the study of meson correlators, and the results
compared with both naive quenched and full dynamical calculations of the same
quantity.Comment: 34 pages (Latex) plus 9 embedded figures; title change
Decay Constants of Heavy-Light Mesons
The decay constants of the heavy-light pseudoscalar mesons are studied in a
high statistics run using the Wilson action at and , and
the clover action at . The systematics of discretisation
errors are discussed. Our best estimates of the decay constants are: =
218(9) MeV, = 1.11(1) and we obtain preliminary values for .Comment: at the Dallas Lattice Conference, October 1993. 3 pages in a single
postscript file, uuencoded form. Rome Preprint 93/98
I=2 Scattering Phase Shift with two Flavors of Improved Dynamical Quarks
We present a lattice QCD calculation of phase shift including the chiral and
continuum extrapolations in two-flavor QCD. The calculation is carried out for
I=2 S-wave scattering. The phase shift is evaluated for two momentum
systems, the center of mass and laboratory systems, by using the finite volume
method proposed by L\"uscher in the center of mass system and its extension to
general systems by Rummukainen and Gottlieb. The measurements are made at three
different bare couplings , 1.95 and 2.10 using a renormalization
group improved gauge and a tadpole improved clover fermion action, and
employing a set of configurations generated for hadron spectroscopy in our
previous work. The illustrative values we obtain for the phase shift in the
continuum limit are (deg.) , and for , and , which are
consistent with experiment.Comment: 40 page
Full QCD simulation on CP-PACS
A status report is made of an on-going full QCD study on the CP-PACS aiming
at a comparative analysis of the effects of improving gauge and quark actions
on hadronic quantities and static quark potential. Simulations are made for
four action combinations, the plaquette or an RG-improved action for gluons and
the Wilson or SW-clover action for quarks, at -1.3GeV and
-0.9. Results demonstrate clearly that the clover
term markedly reduces discretization errors for hadron spectrum, while adding
six-link terms to the plaquette action leads to much better rotational symmetry
in the potential. These results extend experience with quenched simulations to
full QCD.Comment: Talk presented by K. Kanaya at the International Workshop on
``LATTICE QCD ON PARALLEL COMPUTERS'', 10-15 March 1997, Center for
Computational Physics, University of Tsukub
Non-perturbative renormalization of meson decay constants in quenched QCD for a renormalization group improved gauge action
Renormalization constants (-factors) of vector and axial-vector currents
are determined non-perturbatively in quenched QCD for a renormalization group
improved gauge action and a tadpole improved clover quark action using the
Schr\"odinger functional method. Non-perturbative values of -factors turn
out to be smaller than one-loop perturbative values by at lattice
spacing of 1 GeV. The pseudoscalar and vector meson decay
constants calculated with the non-perturbative -factors show a much better
scaling behavior compared to previous results obtained with tadpole improved
one-loop -factors. In particular, the non-perturbative -factors
normalized at infinite physical volume show that scaling violation of the decay
constants are within about 10% up to the lattice spacing GeV.
The continuum estimates obtained from data in the range 1 -- 2 GeV
agree with those determined from finer lattices ( GeV) with the
standard action.Comment: 19 pages, 18 eps figures. Corrected addres
Lattice QCD without topology barriers
As the continuum limit is approached, lattice QCD simulations tend to get
trapped in the topological charge sectors of field space and may consequently
give biased results in practice. We propose to bypass this problem by imposing
open (Neumann) boundary conditions on the gauge field in the time direction.
The topological charge can then flow in and out of the lattice, while many
properties of the theory (the hadron spectrum, for example) are not affected.
Extensive simulations of the SU(3) gauge theory, using the HMC and the closely
related SMD algorithm, confirm the absence of topology barriers if these
boundary conditions are chosen. Moreover, the calculated autocorrelation times
are found to scale approximately like the square of the inverse lattice
spacing, thus supporting the conjecture that the HMC algorithm is in the
universality class of the Langevin equation.Comment: Plain TeX source, 26 pages, 4 figures include
Charmless Two-body Baryonic B Decays
We study charmless two-body baryonic B decays in a diagramatic approach.
Relations on decay amplitudes are obtained. In general there are more than one
tree and more than one penguin amplitudes. The number of independent amplitudes
can be reduced in the large m_B limit. It leads to more predictive results.
Some prominent modes for experimental searches are pointed out.Comment: 15 pages, 2 figures. To appear in Phys. Rev.
Radial Correlations between two quarks
In nuclear many-body problems the short-range correlation between two
nucleons is well described by the corresponding correlation in the {two}-body
problem. Therefore, as a first step in any attempt at an analogous description
of many-quark systems, it is necessary to know the two-quark correlation. With
this in mind, we study the light quark distribution in a heavy-light meson with
a static heavy quark. The charge and matter radial distributions of these
heavy-light mesons are measured on a lattice with a light quark mass about that
of the strange quark. Both distributions can be well fitted upto r approx 0.7
fm with the exponential form w_i^2(r), where w_i(r)=A exp(-r/r_i). For the
charge(c) and matter(m) distributions r_c approx 0.32(2) fm and r_m \approx
0.24(2) fm. We also discuss the normalisation of the total charge (defined to
be unity in the continuum limit) and matter integrated over all space, finding
1.30(5) and 0.4(1) respectively for a lattice spacing approx 0.17 fm.Comment: 8 pages, 3 ps figure
The Semileptonic Decays and from Lattice QCD
We present a lattice QCD calculation of the form factors and differential
decay rates for semileptonic decays of the heavy-light mesons and to
the final state . The results are obtained with three methodological
improvements over previous lattice calculations: a matching procedure that
reduces heavy-quark lattice artifacts, the first study of lattice-spacing
dependence, and the introduction of kinematic cuts to reduce model dependence.
We show that the main systematics are controllable (within the quenched
approximation) and outline how the calculations could be improved to aid
current experiments in the determination of~ and~.Comment: 35 pp, 12 fig
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