290 research outputs found
Ab Initio Study of Hybrid b-bar-gb Mesons
Hybrid b-bar-gb molecules in which the heavy b-bar-b pair is bound together
by the excited gluon field g are studied using the Born-Oppenheimer expansion
and numerical simulations. The consistency of results from the two approaches
reveals a simple and compelling physical picture for heavy hybrid states.Comment: 4 pages, 3 figures, uses REVTeX and epsf, final published versio
Unquenched Charmonium with NRQCD - Lattice 2000
We present results from a series of NRQCD simulations of the charmonium
system, both in the quenched approximation and with n_f = 2 dynamical quarks.
The spectra show evidence for quenching effects of ~10% in the S- and
P-hyperfine splittings. We compare this with other systematic effects.
Improving the NRQCD evolution equation altered the S-hyperfine by as much as 20
MeV, and we estimate radiative corrections may be as large as 40%.Comment: Lattice 2000 (Heavy Quark Physics
Measuring the aspect ratio renormalization of anisotropic-lattice gluons
Using tadpole inproved actions we investigate the consistency between
different methods of measuring the aspect ratio renormalization of
anisotropic-lattice gluons for bare aspect ratios \chi_0=4,6,10 and inverse
lattice spacing in the range a_s^{-1}=660-840 MeV. The tadpole corrections to
the action, which are established self-consistently, are defined for two cases,
mean link tadpoles in Landau gauge and gauge invariant mean plaquette tadpoles.
Parameters in the latter case exhibited no dependence on the spatial lattice
size, L, while in the former, parameters showed only a weak dependence on L
easily extrapolated to L=\infty.
The renormalized anisotropy \chi_R was measured using both the torelon
dispersion relation and the sideways potential method. We found good agreement
between these different approaches. Any discrepancy was at worst 3-4% which is
consistent with the effect of lattice artifacts that for the torelon we
estimate as O(\a_Sa_s^2/R^2) where R is the flux-tube radius.
We also present some new data that suggests that rotational invariance is
established more accurately for the mean-link action than the plaquette action.Comment: LaTeX 18 pages including 7 figure
Tadpole renormalization and relativistic corrections in lattice NRQCD
We make a comparison of two tadpole renormalization schemes in the context of
the quarkonium hyperfine splittings in lattice NRQCD. Improved gauge-field and
NRQCD actions are analyzed using the mean-link in Landau gauge, and
using the fourth root of the average plaquette . Simulations are done
for , , and systems. The hyperfine splittings are
computed both at leading and at next-to-leading order in the relativistic
expansion. Results are obtained at lattice spacings in the range of about
0.14~fm to 0.38~fm. A number of features emerge, all of which favor tadpole
renormalization using . This includes much better scaling behavior of
the hyperfine splittings in the three quarkonium systems when is
used. We also find that relativistic corrections to the spin splittings are
smaller when is used, particularly for the and
systems. We also see signs of a breakdown in the NRQCD expansion when the bare
quark mass falls below about one in lattice units. Simulations with
also appear to be better behaved in this context: the bare quark masses turn
out to be larger when is used, compared to when is used on
lattices with comparable spacings. These results also demonstrate the need to
go beyond tree-level tadpole improvement for precision simulations.Comment: 14 pages, 7 figures (minor changes to some phraseology and
references
O(a)-improved quark action on anisotropic lattices and perturbative renormalization of heavy-light currents
We investigate the Symanzik improvement of the Wilson quark action on
anisotropic lattices. Taking first a general action with nearest-neighbor and
clover interactions, we study the mass dependence of the ratio of the hopping
parameters, the clover coefficients, and an improvement coefficient for
heavy-light vector and axial vector currents. We show how tree-level
improvement can be achieved. For a particular choice of the spatial Wilson
coupling, the results simplify, and improvement is possible.
(Here is the bare quark mass and the temporal lattice spacing.)
With this choice we calculate the renormalization factors of heavy-light
bilinear operators at one-loop order of perturbation theory employing the
standard plaquette gauge action.Comment: 26 pages, 8 figure
Desempenho de cultivares de milho em áreas de arroz irrigado do Rio Grande do Sul nas safras 2002/03 e 2003/04.
bitstream/item/33528/1/documento-131.pd
Comparison Studies of Finite Momentum Correlators on Anisotropic and Isotropic Lattices
We study hadronic two- and three-point correlators relevant for heavy to
light pseudoscalar meson semi-leptonic decays, using Symanzik improved glue,
D234 light quark and NRQCD heavy quark actions. Detailed comparisons are made
between simulations on anisotropic and isotropic lattices involving finite
momentum hadrons. We find evidence that having an anisotropy helps in
extracting better signals at higher momenta. Initial results for the form
factors f_+(q^2) and f_0(q^2) are presented with tree-level matching of the
lattice heavy-light currents.Comment: 43 pages with 50 postscript figure
Heavy Quarks on Anisotropic Lattices: The Charmonium Spectrum
We present results for the mass spectrum of mesons simulated on
anisotropic lattices where the temporal spacing is only half of the
spatial spacing . The lattice QCD action is the Wilson gauge action plus
the clover-improved Wilson fermion action. The two clover coefficients on an
anisotropic lattice are estimated using mean links in Landau gauge. The bare
velocity of light has been tuned to keep the anisotropic, heavy-quark
Wilson action relativistic. Local meson operators and three box sources are
used in obtaining clear statistics for the lowest lying and first excited
charmonium states of , , , and . The
continuum limit is discussed by extrapolating from quenched simulations at four
lattice spacings in the range 0.1 - 0.3 fm. Results are compared with the
observed values in nature and other lattice approaches. Finite volume effects
and dispersion relations are checked.Comment: 36 pages, 6 figur
Gauge Theories on a 2+2 Anisotropic Lattice
The implementation of gauge theories on a four-dimensional anisotropic
lattice with two distinct lattice spacings is discussed, with special attention
to the case where two axes are finely and two axes are coarsely discretized.
Feynman rules for the Wilson gauge action are derived and the renormalizability
of the theory and the recovery of the continuum limit are analyzed. The
calculation of the gluon propagator and the restoration of Lorentz invariance
in on-shell states is presented to one-loop order in lattice perturbation
theory for on both 2+2 and 3+1 lattices.Comment: 27 pages, uses feynmf. Font compatibility adjuste
Heavy-light Mesons and Baryons with b quarks
We present lattice results for the spectrum of mesons containing one heavy
quark and of baryons containing one or two heavy quarks. The calculation is
done in the quenched approximation using the NRQCD formalism for the heavy
quark. We analyze the dependence of the mass splittings on both the heavy and
the light quark masses. Meson P-state fine structure and baryon hyperfine
splittings are resolved for the first time. We fix the b quark mass using both
M_B and M_{\Lambda_b}, and our best estimate is m_b^\MSbar(m_b^\MSbar) =
4.35(10)({}^{-3}_{+2})(10) GeV. The spectrum, obtained by interpolation to m_b,
is compared with the experimental data.Comment: 34 pages, LaTeX, 13 postscript figures, version as publish in Phys.
Rev.
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