9,723 research outputs found
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
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
P-wave Radial distributions of a Heavy-light meson on a lattice
This is a follow-up to our earlier work for the charge (vector) and matter
(scalar) distributions for S-wave states in a heavy-light meson, where the
heavy quark is static and the light quark has a mass about that of the strange
quark. The calculation is again carried out with dynamical fermions on a
16^3x24 lattice with a lattice spacing of about 0.14 fm. It is shown that
several features of the S- and P-wave distributions are in qualitative
agreement with what one expects from a simple one-body Dirac equation
interpretation.Comment: 5 pages, 2 figures, Quark Confinement and the Hadron Spectrum VI,
Sardinia, Italy, September, 200
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The Charge and Matter radial distributions of Heavy-Light mesons calculated on a lattice
For a heavy-light meson with a static heavy quark, we can explore the light
quark distribution. The charge and matter radial distributions of these
heavy-light mesons are measured on a 16^3 * 24 lattice at beta=5.7 and a
hopping parameter corresponding to a light quark mass about that of the strange
quark. Both distributions can be well fitted up to 4 lattice spacings (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 and matter
integrated over all space, finding 1.30(5) and 0.4(1) respectively.Comment: 31 pages including 7 ps figure
Breaking the cycle? The effect of education on welfare receipt among children of welfare recipients
We examine the impact of high school graduation on the probability individuals from welfare backgrounds use welfare themselves. Our data consists of administrative educational records for grade 12 students in a Canadian province linked with their own and their parents' welfare records. We address potential endogeneity problems by: 1) controlling for ability using past test scores; 2) using an instrument for graduation based on school principal fixed effects; and 3) using a Heckman- Singer type unobserved heterogeneity estimator. Graduation would reduce welfare receipt of dropoutsby Ăť to 3/4. Effects are larger for individuals from troubled family backgrounds and low income neighbourhoods.
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