56 research outputs found
Quark-quark correlations and baryon electroweak observables
The simple independent quark models have difficulties explaining
simultaneously the totality of the known hyperon magnetic moments and hyperon
semi-leptonic decay rates. We show that both the Goldstone boson loop
contributions and the two-quark effective exchange currents are essential in
explaining these observables.Comment: 7 pages, 1 figur
The proton spin sum rule chiral bag prediction, an update
We reevaluate a quark model prediction using the new QCD evolution function
calculated to the 3 loop order and conclude that this model compares favorably
with the new experimental results.Comment: 10 pages, 2 figures available by request, give fax numbe
Isgur - Wise Functions for Confined Light Quarks in a Colour Electric Potential
We explore the influence on the Isgur-Wise function of the colour electric
potential between heavy and light quarks in mesons. It is shown that in bag
models, its inclusion tends to restore light quark flavour symmetry relative to
the MIT bag predictions, and that relative to this model it flattens the
Isgur-Wise function. Results compare very well with observations.Comment: 9 pages, 1 figure (available upon request), Latex, TPJU - 4/9
On Quarks and Flavour Symmetry
Hadronic spectroscopy can be introduced to students and developed rather far
without requiring SU(N) flavour symmetry. In such a "minimalist" presentation,
we are naturally led to comment and clarify the concept of the "generalized"
Pauli principle
A chromomagnetic mechanism for the X(3872) resonance
The chromomagnetic interaction, with proper account for flavour-symmetry
breaking, is shown to explain the mass and coupling properties of the X(3872)
resonance as a = 1 state consisting of a heavy quark-antiquark
pair and a light one. It is crucial to introduce all the spin-colour
configurations compatible with these quantum numbers and diagonalise the
chromomagnetic interaction in this basis. This approach thus differs from the
molecular picture and from the diquark-antidiquark picture.Comment: 4 pages - revtex4 - Typos corrected, refs. added, to be published in
Phys. Rev.
Gluelump Spectrum in the Bag Model
We explore the ordering of the lowest levels in a simple bag model of the
``gluelump'' of Michael and also discuss, again within the context of the bag
model, the related problem of hybrid potentials in the limit of very small
spacing between quark and anti-quark sources.Comment: 10 page
Chiral QCD, General QCD Parameterization and Constituent Quark Models
Several recent papers -using effective QCD chiral Lagrangians- reproduced
results obtained with the general QCD parameterization (GP). These include the
baryon 8+10 mass formula, the octet magnetic moments and the coincidental
nature of the "perfect" -3/2 ratio between the magnetic moments of p and n.
Although we anticipated that the GP covers the case of chiral treatments, the
above results explicitly exemplify this fact. Also we show by the GP that -in
any model or theory (chiral or non chiral) reproducing the results of exact
QCD- the Franklin (Coleman Glashow) sum rule for the octet magnetic moments
must be violated.Comment: 10 pages, Latex; abridged version (same results), removed some
reference
Electromagnetic transition form factors of negative parity nucleon resonances
We have calculated the transition form factors for the electromagnetic
excitation of the negative parity resonances of the nucleon using different
models previously proposed and we discuss their results and limits by
comparison with experimental data.Comment: 13 pages, 6 figures, to be published on Journal of Physics
Search for Flavoured Multiquarks in a Simple Bag Model
We use a bag model to study flavoured mesonic and baryonic
states, where one heavy quark is associated with
light quarks or antiquarks, and search for possible stable multiquarks. No
bound state is found. However some states lie not too high above their
dissociation threshold, suggesting the possibility of resonances, or perhaps
bound states in improved models.Comment: REVTEX, VERSION 3.
A Naturally Narrow Positive Parity Theta^+
We present a consistent color-flavor-spin-orbital wave function for a
positive parity Theta^+ that naturally explains the observed narrowness of the
state. The wave function is totally symmetric in its flavor-spin part and
totally antisymmetric in its color-orbital part. If flavor-spin interactions
dominate, this wave function renders the positive parity Theta^+ lighter than
its negative parity counterpart. We consider decays of the Theta^+ and compute
the overlap of this state with the kinematically allowed final states. Our
results are numerically small. We note that dynamical correlations between
quarks are not necessary to obtain narrow pentaquark widths.Comment: 10 pages, 1 figure, Revtex4, two-column format, version to be
published in Phys. Rev. D, includes numerical estimates of decay width
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