72 research outputs found
A Study of Degenerate Four-quark states in SU(2) Lattice Monte Carlo
The energies of four-quark states are calculated for geometries in which the
quarks are situated on the corners of a series of tetrahedra and also for
geometries that correspond to gradually distorting these tetrahedra into a
plane. The interest in tetrahedra arises because they are composed of {\bf
three } degenerate partitions of the four quarks into two two-quark colour
singlets. This is an extension of earlier work showing that geometries with
{\bf two} degenerate partitions (e.g.\ squares) experience a large binding
energy. It is now found that even larger binding energies do not result, but
that for the tetrahedra the ground and first excited states become degenerate
in energy. The calculation is carried out using SU(2) for static quarks in the
quenched approximation with on a lattice. The
results are analysed using the correlation matrix between different euclidean
times and the implications of these results are discussed for a model based on
two-quark potentials.Comment: Original Raw PS file replace by a tarred, compressed and uuencoded PS
fil
Orbitally excited and hybrid mesons from the lattice
We discuss in general the construction of gauge-invariant non-local meson
operators on the lattice. We use such operators to study the - and -wave
mesons as well as hybrid mesons in quenched QCD, with quark masses near the
strange quark mass. The resulting spectra are compared with experiment for the
orbital excitations. For the states produced by gluonic excitations (hybrid
mesons) we find evidence of mixing for non-exotic quantum numbers. We give
predictions for masses of the spin-exotic hybrid mesons with $J^{PC}=1^{-+},\
0^{+-}2^{+-}$.Comment: 31 pages, LATEX, 8 postscript figures. Reference adde
The Spectrum of the Hybrid Mesons with Heavy Quarks from the B.S. Equation
We construct the B.S. equation for the hybrid mesons under instantaneous
approximation. The kernel is chosen as the sum of an one-gluon exchange
potential and a linear confining potential. The equations are solved by
numerical method, and the spectrum of hybrid mesons and
are obtained.Comment: 11 pages, latex, 3 figure
Efficient Hadronic Operators in Lattice Gauge Theory
We study operators to create hadronic states made of light quarks in quenched
lattice gauge theory. We construct non-local gauge-invariant operators which
provide information about the spatial extent of the ground state and excited
states. The efficiency of the operators is shown by looking at the wave
function of the first excited state, which has a node as a function of the
spatial extent of the operator. This allows one to obtain an uncontaminated
ground state for hadrons.Comment: 18 pages, Latex text, followed by 11 postscript figures in
self-unpacking file. Also available at
ftp://suna.amtp.liv.ac.uk/pub/cmi/wavefn
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
Topological Structure of the SU(3) Vacuum
We investigate the topological structure of the vacuum in SU(3) lattice gauge
theory. We use under-relaxed cooling to remove the high-frequency fluctuations
and a variety of "filters" to identify the topological charges in the resulting
smoothened field configurations. We find a densely packed vacuum with an
average instanton size, in the continuum limit, of about 0.5 fm. The density at
large sizes decreases as a large inverse power of the size. At small sizes we
see some sign of a trend towards the asymptotic perturbative behaviour. We find
that an interesting polarisation phenomenon occurs: the large topological
charges tend to have, on the average, the same sign and are over-screened by
the smaller charges which tend to have, again on the average, the opposite sign
to the larger instantons. We also calculate the topological susceptibility for
which we obtain a continuum value of about 187 MeV. We perform the calculations
for various volumes, lattice spacings and numbers of cooling sweeps, so as to
obtain some control over the associated systematic errors. The coupling range
is from beta=6.0 to beta=6.4 and the lattice volumes range from 16x16x16x48 to
32x32x32x64.Comment: LaTeX. Self-unpacking, uuencoded tar-compressed fil
Hybrid meson decay from the lattice
We discuss the allowed decays of a hybrid meson in the heavy quark limit. We
deduce that an important decay will be into a heavy quark non-hybrid state and
a light quark meson, in other words, the de-excitation of an excited gluonic
string by emission of a light quark-antiquark pair.
We discuss the study of hadronic decays from the lattice in the heavy quark
limit and apply this approach to explore the transitions from a spin-exotic
hybrid to and where is a scalar meson. We obtain a
signal for the transition emitting a scalar meson and we discuss the
phenomenological implications.Comment: 18 pages, LATEX, 3 ps figure
Four-quark flux distribution and binding in lattice SU(2)
The full spatial distribution of the color fields of two and four static
quarks is measured in lattice SU(2) field theory at separations up to 1 fm at
beta=2.4. The four-quark case is equivalent to a qbar q qbar q system in SU(2)
and is relevant to meson-meson interactions. By subtracting two-body flux tubes
from the four-quark distribution we isolate the flux contribution connected
with the four-body binding energy. This contribution is further studied using a
model for the binding energies. Lattice sum rules for two and four quarks are
used to verify the results.Comment: 46 pages including 71 eps figures. 3D color figures are available at
www.physics.helsinki.fi/~ppennane/pics
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