199 research outputs found
Universal few-body physics in a harmonic trap
Few-body systems with resonant short-range interactions display universal
properties that do not depend on the details of their structure or their
interactions at short distances. In the three-body system, these properties
include the existence of a geometric spectrum of three-body Efimov states and a
discrete scaling symmetry. Similar universal properties appear in 4-body and
possibly higher-body systems as well. We set up an effective theory for
few-body systems in a harmonic trap and study the modification of universal
physics for 3- and 4-particle systems in external confinement. In particular,
we focus on systems where the Efimov effect can occur and investigate the
dependence of the 4-body spectrum on the experimental tuning parameters.Comment: 20 pages, 10 figures, final version, new references adde
Helicity amplitudes and electromagnetic decays of strange baryon resonances
We present results for the helicity amplitudes of the lowest-lying hyperon
resonances Y*, computed within the framework of the Bonn constituent-quark
model, which is based on the Bethe-Salpeter approach. The seven parameters
entering the model are fitted against the best known baryon masses.
Accordingly, the results for the helicity amplitudes are genuine predictions.
Some hyperon resonances are seen to couple more strongly to a virtual photon
with finite Q^2 than to a real photon. Other Y*'s, such as the S_{01}(1670)
Lambda resonance or the S_{11}(1620) Sigma resonance, have large
electromagnetic decay widths and couple very strongly to real photons. The
negatively-charged and neutral members of a Sigma* triplet may couple only
moderately to the Sigma(1193), while the positively-charged member of the same
Sigma* triplet displays a relatively large coupling to the Sigma^+(1193) state.
This illustrates the necessity of investigating all isospin channels in order
to obtain a complete picture of the hyperon spectrum.Comment: 4 pages, 1 figure, 1 table, Proceedings of the Conference
"International Workshop on the Physics of Excited Baryons NSTAR 05",
Tallahassee, Florida (USA), Oct. 2005, contributed tal
Quark-Model Identification of Baryon Ground and Resonant States
We present a new classification scheme of baryon ground states and resonances
into SU(3) flavor multiplets. The scheme is worked out along a covariant
formalism with relativistic constituent quark models and it relies on detailed
investigations of the baryon spectra, the spin-flavor structure of the baryon
eigenstates, the behaviour of their probability density distributions as well
as covariant predictions for mesonic decay widths. The results are found to be
quite independent of the specific types of relativistic constituent quark
models employed. It turns out that a consistent classification requires to
include also resonances that are presently reported from experiment with only
two-star status.Comment: 24 pages, 20 Fig
Relativistic quark models of baryons with instantaneous forces
This is the first of a series of three papers treating light baryon resonances (up to 3 GeV) within a relativistically covariant quark model based on the three-fermion Bethe-Salpeter equation with instantaneous two- and three-body forces. In this paper we give a unified description of the theoretical background and demonstrate how to solve the Bethe-Salpeter equation by a reduction to the Salpeter equation. The specific new features of our covariant Salpeter model with respect to the usual nonrelativistic quark model are discussed in detail. The purely theoretical results obtained in this paper will be applied numerically to explicit quark models for light baryons in two subsequent papers
Static observables of relativistic three-fermion systems with instantaneous interactions
We show that static properties like the charge radius and the magnetic moment
of relativistic three-fermion bound states with instantaneous interactions can
be formulated as expectation values with respect to intrinsically defined
wavefunctions. The resulting operators can be given a natural physical
interpretation in accordance with relativistic covariance. We also indicate how
the formalism may be generalized to arbitrary moments. The method is applied to
the computation of static baryon properties with numerical results for the
nucleon charge radii and the baryon octet magnetic moments. In addition we make
predictions for the magnetic moments of some selected nucleon resonances and
discuss the decomposition of the nucleon magnetic moments in contributions of
spin and angular momentum, as well as the evolution of these contributions with
decreasing quark mass.Comment: 13 pages, including 2 figures and 3 tables, submitted to Eur.Phys.J.
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