140 research outputs found
in a chiral constituent quark model and its interpolating fields
The recently discovered pentaquark is described within the chiral
constituent quark model. Within this picture the flavor-spin interaction
between valence quarks inverts the and levels of the
four-quark subsystem and consequently the lowest-lying pentaquark is a positive
parity, I=0, J=1/2 state of the flavor antidecuplet, similar to the soliton
model prediction. Contrary to the soliton model, however, the quark picture
predicts its spin-orbit partner with . Different interpolating fields
intended for lattice calculations of are constructed, which have a
maximal overlap with this baryon if it is indeed a quark excitation in the 5Q
system.Comment: 9 p
Extended Goldstone-Boson-Exchange Constituent Quark Model
We present an extension of the Goldstone-boson-exchange constituent quark
model including additional interactions beyond the ones used hitherto. For the
hyperfine interaction between the constituent quarks we assume pseudoscalar,
vector, and scalar meson exchanges and consider all relevant force components
produced by these types of exchanges. The resulting model, which corresponds to
a relativistic Poincare-invariant Hamiltonian (or equivalently mass operator),
provides a unified framework for a covariant description of all light and
strange baryons. The ground states and resonances up to an excitation energy of
about 2 GeV are reproduced in fair agreement with phenomenology, with the
exception of the first excitations above the Lambda and Xi ground states.Comment: 11 pages, 4 figures, 3 tables; substantial revisions, additional
author, bibliography extended and update
Local Current Operators for Arbitrary Spin Particles
Free current operators are constructed for massive particles with arbitrary
spin . Such current operators are related to representations of the U(N,N)
type groups and are covariant under the (extended) Poincar\'{e} group and
charge conjugation, where the charge conjugation operation is defined as an
automorphism on U(N,N) elements. The currents are also required to satisfy
current conservation, hermiticity, and locality. The condition that the
currents be local is shown to be equivalent to certain integral constraints on
form factors. These constraints are satisfied by writing the currents in terms
of free local spin fields. It is shown that there are different
local currents for a spin particle, each with an arbitrary form factor,
generalizing the Dirac and Pauli currents for spin 1/2 particles. Static
properties of the various currents are also given.Comment: 25 page
Strong Decays of N and Delta Resonances in the Point-Form Formalism
We present covariant predictions of relativistic constituent quark models for
pi and eta decay widths of N and Delta resonances. The results are calculated
for a model decay operator within the point-form spectator approximation. It is
found that most theoretical values underestimate the experimental data
considerably.Comment: 4 pages; Proceedings for N*2004, Grenoble, March 24-27 (2004
Nucleon magnetic moments in an extended chiral constituent quark model
We present results for the nucleon magnetic moments in the context of an
extended chiral constituent quark model based on the mechanism of the Goldstone
boson exchange, as suggested by the spontaneous breaking of chiral symmetry in
QCD. The electromagnetic charge-current operator is consistently deduced from
the model Hamiltonian, which includes all force components for the
pseudoscalar, vector and scalar meson exchanges. Thus, the continuity equation
is satisfied for each piece of the interaction, avoiding the introduction of
any further parameter. A good agreement with experimental values is found. The
role of isoscalar two-body operators, not constrained by the continuity
equation, is also investigated.Comment: 7 pages, 1 table, submitted for publication to Phys. Lett. B,
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