882 research outputs found
Negative parity baryons in the expansion: the three towers of states revisited
We discuss the compatibility between the quark-shell picture and the
meson-nucleon scattering picture in large QCD for mixed symmetric
= 1 states previously analyzed by using a simple Hamiltonian including
operators up to order defined in the standard ground state
symmetric core + excited quark procedure. Here we introduce a Hamiltonian of
order defined in a new approach where the separation of
the system into two parts is not required. Three degenerate sets of states
(towers) with the same quantum numbers as in the scattering picture and in the
standard procedure are obtained. Thus the 0 is equally achieved. The
eigenvalues of the presently chosen Hamiltonian also have simple analytic
expressions, depending linearly on the three dynamical coefficients entering
the Hamiltonian. This reinforces the validity of the new approach which had
already 0 described excited negative parity baryons in a large energy range.Comment: 13 page
SU(6) baryon multiplet in the expansion
The masses of excited states of mixed orbital symmetry of nonstrange and
strange baryons belonging to the lowest multiplet are
calculated in the expansion to order with a new method which
allows to considerably reduce the number of linearly independent operators
entering the mass formula. This study represents an extension to SU(6) of our
work on nonstrange baryons, the framework of which was SU(4). The conclusion
regarding the role of the flavor operator, neglected in previous SU(6) studies,
is reinforced. Namely, both the flavor and spin operators contribute dominantly
to the flavor-spin breaking.Comment: 26 pages, 11 tables, to be published in PR
Group theoretical study of nonstrange and strange mixed symmetric baryon states in the expansion
Using group theory arguments we extend and complete our previous work by
deriving all SU(6) exact wave functions associated to the spectrum of mixed
symmetric baryon states in the expansion. The extension to
SU(6) enables us to study the mass spectra of both strange and nonstrange
baryons, while previous work was restricted to nonstrange baryons described by
SU(4). The wave functions are specially written in a form to allow a comparison
with the approximate, customarily used wave functions, where the system is
separated into a ground state core and an excited quark. We show that the
matrix elements of the flavor operator calculated with the exact wave functions
acquire the same asymptotic form at large , irrespective of the
spin-flavor multiplet contained in , while with the approximate wave
function one cannot obtain a similar behaviour. The isoscalar factors of the
permutation group of particles derived here can be used in any problem
where a given fermion system is described by the partition , and one
fermion has to be separated from the rest.Comment: 19 pages, 7 tables, comments added in the introduction and in the
section 3, to be published in Phys. Rev.
Mass formula for strange baryons in large QCD versus quark model
A previous work establishing a connection between a quark model, with
relativistic kinematics and a -confinement plus one gluon exchange, and the
expansion mass formula is extended to strange baryons. Both methods
predict values for the SU(3)-breaking mass terms which are in good agreement
with each other. Strange and nonstrange baryons are shown to exhibit Regge
trajectories with an equal slope, but with an intercept depending on the
strangeness. Both approaches agree on the value of the slope and of the
intercept and on the existence of a single good quantum number labeling the
baryons within a given Regge trajectory.Comment: 2 figure
Probabilities in nonorthogonal basis: Four--quark systems
Four-quark states may exist as colorless meson-meson molecules or compact
systems with two-body colored components. We derive an analytical procedure to
expand an arbitrary four--quark wave function in terms of nonorthogonal color
singlet--singlet vectors. Using this expansion we develop the necessary
formalism to evaluate the probability of physical components with an arbitrary
four-quark wave function. Its application to characterize bound and unbound
four--quark states as meson-meson, molecular or compact systems is discussedComment: Accepted for publication in PR
Anti-charmed pentaquark from B decays
We explore the possibility of observing the anti-charmed pentaquark state
from the decay of meson produced at -factory
experiments. We first show that the observed branching ratio of the to , as well as its open histograms, can be remarkably well
explained by assuming that the decay proceeds first through the (or ) decay, whose branching ratios are known, and
then through the subsequent decay of the virtual or
mesons to , whose strength are calculated using previously fit
hadronic parameters. We then note that the can be similarly produced
when the virtual or decay into an anti-nucleon and a
. Combining the present theoretical estimates for the ratio and , we find that the anti-charmed pentaquark , which was
predicted to be bound by several model calculations, can be produced via , and be observed from the -factory experiments
through the weak decay of .Comment: 4 pages, 4 figures, Revised version to be published in Physical
Review Letter
k-String tensions and the 1/N expansion
We address the question of whether the large-N expansion in pure SU(N) gauge
theories requires that k-string tensions must have a power series expansion in
1/N^2, as in the sine law, or whether 1/N contributions are also allowable, as
in Casimir scaling. We find that k-string tensions may, in fact, have 1/N
corrections, and consistency with the large-N expansion in the open-string
sector depends crucially on an exact cancellation, which we will prove, among
terms involving odd powers of 1/N in particular combinations of Wilson loops.
It is shown how these cancellations are fulfilled, and consistency with the
large-N expansion achieved, in a concrete example, namely, strong-coupling
lattice gauge theory with the heat-kernel action. This is a model which has
both a 1/N^2 expansion and Casimir scaling of the k-string tensions. Analysis
of the closed string channel in this model confirms our conclusions, and
provides further insights into the large-N dependence of energy eigenstates and
eigenvalues.Comment: RevTeX4, 21 pages. Typos corrected, references added, some
discussions expanded; conclusions unchanged. Version to appear on PR
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