74 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.
A one parameter representation for the Isgur-Wise function
We use a lattice QCD heavy-light wavefunction to generate a single
parameter, model independent description of the Isgur-Wise function. Using
recent data we find the zero-recoil slope to be , while
the second derivative turns out to be .Comment: Latex (uses epsf macro), 7 pages of text, 2 postscript figures
included
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
Two-electron atoms, ions and molecules
The quantum mechanics of two-electron systems is reviewed, starting with the
ground state of the helium atom and helium-like ions, with central charge . For Z=1, demonstrating the stability of the negative hydrogen ion, H,
cannot be achieved using a mere product of individual electron wave functions,
and requires instead an explicit account for the anticorrelation among the two
electrons. The wave function proposed by Chandrasekhar is revisited, where the
permutation symmetry is first broken and then restored by a counter-term. More
delicate problems can be studied using the same strategy: the stability of
hydrogen-like ions for any value of the proton-to-electron mass
ratio ; the energy of the lowest spin-triplet state of helium and
helium-like ions; the stability of the doubly-excited hydrogen ion with
unnatural parity. The positronium molecule , which has been
predicted years ago and discovered recently, can also be shown to be stable
against spontaneous dissociation, though the calculation is a little more
involved. Emphasis is put on symmetry breaking which can either spoil or
improve the stability of systems.Comment: 16 pages, 2 figure
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
Phenomenology of the Pentaquark Antidecuplet
We consider the mass splittings and strong decays of members of the
lowest-lying pentaquark multiplet, which we take to be a parity-odd
antidecuplet. We derive useful decompositions of the quark model wave functions
that allow for easy computation of color-flavor-spin matrix elements. We
compute mass splittings within the antidecuplet including spin-color and
spin-isospin interactions between constituents and point out the importance of
hidden strangeness in rendering the nucleon-like states heavier than the S=1
state. Using recent experimental data on a possible S=1 pentaquark state, we
make decay predictions for other members of the antidecuplet.Comment: 12 pages LaTeX, 1 eps figur
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