100 research outputs found
QCD on Coarse Lattices
We show that the perturbatively-improved gluon action for QCD, once it is
tadpole-improved, gives accurate results even with lattice spacings as large as
0.4~fm. {\em No\/} tuning of the couplings is required. Using this action and
lattice spacing, we obtain a static potential that is rotationally invariant to
within a few percent, the spin-averaged charmonium spectrum accurate to within
30--40~MeV, and scaling to within 5--10\%. We demonstrate that simulations on
coarse lattices are several orders of magnitude less costly than simulations
using current methods.Comment: 4 page
First results from the asymmetric O(a) improved Fermilab action
We present first results from calculations using O(a) improved (FNAL)
space-time asymmetric action on a 12^3 x 24 quenched lattice at \beta = 5.7 and
c_SW = 1.57. The asymmetry parameter is determined non-perturbatively from the
energy-momentum dispersion relation. This improvement scheme is mass dependent,
and the calculations have been done in the charm and bottom quark mass sectors
since it is at these heavier masses that the asymmetry is expected to be
relevant.Comment: 3 pp. LaTeX2e, 6PostScript figures, uses espcrc2.sty. Contribution to
Lattice99 (Pisa) proceedings (Improvement and Renormalisation
A More Improved Lattice Action for Heavy Quarks
We extend the Fermilab formalism for heavy quarks to develop a more improved
action. We give results of matching calculations of the improvement couplings
at tree level. Finally, we estimate the discretization errors associated with
the new action.Comment: 3 pages, 1 figure, Lattice 2003 Tsukuba Japa
Constrained Curve Fitting
We survey techniques for constrained curve fitting, based upon Bayesian
statistics, that offer significant advantages over conventional techniques used
by lattice field theorists.Comment: Lattice2001(plenary); plenary talk given by G.P. Lepage at Lattice
2001 (Berlin); 9 pages, 5 figures (postscript specials
Estimated Errors in |Vcd|/|Vcs| from Semileptonic D Decays
We estimate statistical and systematic errors in the extraction of the CKM
ratio |Vcd|/|Vcs| from exclusive D-meson semileptonic decays using lattice QCD
and anticipated new experimental results.Comment: LATTICE98(heavyqk), LaTeX, 3 pages, 2 postscript figures, uses
espcrc2.sty and hyperbasics.te
Lattice QCD on Small Computers
We demonstrate that lattice QCD calculations can be made -- times
faster by using very coarse lattices. To obtain accurate results, we replace
the standard lattice actions by perturbatively-improved actions with
tadpole-improved correction terms that remove the leading errors due to the
lattice. To illustrate the power of this approach, we calculate the
static-quark potential, and the charmonium spectrum and wavefunctions using a
desktop computer. We obtain accurate results that are independent of the
lattice spacing and agree well with experiment.Comment: 15 pages, 3 figs incl as LaTex pictures Minor additions to tables and
tex
Light Quark Masses with an O(a)-Improved Action
We present the recent Fermilab calculations of the masses of the light
quarks, using tadpole-improved Sheikholeslami-Wohlert (SW) quarks. Various
sources of systematic errors are studied. Our final result for the average
light quark mass in the quenched approximation evaluated in the
scheme is .Comment: 3 pgs. 3 figures. espcrc2.sty included. Talk presented at
LATTICE96(phenomenology
A precise determination of the Bc mass from dynamical lattice QCD
We perform a precise calculation of the mass of the B_c meson using
unquenched configurations from the MILC collaboration including 2+1 flavours of
improved staggered quarks. Lattice NRQCD and the Fermilab formalism are used to
describe the b and c quarks respectively. We find the mass of the B_c meson to
be 6.304(16) GeVComment: Talk presented at Lattice2004(heavy), Fermilab, June 21-26. 3 pages,
2 figure
Theta-terms in nonlinear sigma-models
We trace the origin of theta-terms in non-linear sigma-models as a
nonperturbative anomaly of current algebras. The non-linear sigma-models emerge
as a low energy limit of fermionic sigma-models. The latter describe Dirac
fermions coupled to chiral bosonic fields. We discuss the geometric phases in
three hierarchies of fermionic sigma-models in spacetime dimension (d+1) with
chiral bosonic fields taking values on d-, d+1-, and d+2-dimensional spheres.
The geometric phases in the first two hierarchies are theta-terms. We emphasize
a relation between theta-terms and quantum numbers of solitons.Comment: 10 pages, no figures, revtex, typos correcte
Perturbative two- and three-loop coefficients from large beta Monte Carlo
Perturbative coefficients for Wilson loops and the static quark self-energy
are extracted from Monte Carlo simulations at large beta on finite volumes,
where all the lattice momenta are large. The Monte Carlo results are in
excellent agreement with perturbation theory through second order. New results
for third order coefficients are reported. Twisted boundary conditions are used
to eliminate zero modes and to suppress Z_3 tunneling.Comment: 6 pages, 5 figures. Contributions of Howard Trottier and Paul
Mackenzie to Lattice '9
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