240 research outputs found
Covariant calculation of strange decays of baryon resonances
We present results for kaon decay widths of baryon resonances from a
relativistic study with constituent quark models. The calculations are done in
the point-form of Poincare-invariant quantum mechanics with a spectator-model
decay operator. We obtain covariant predictions of the Goldstone-boson-exchange
and a variant of the one-gluon-exchange constituent quark models for all kaon
decay widths of established baryon resonances. They are generally characterized
by underestimating the available experimental data. In particular, the widths
of kaon decays with increasing strangeness in the baryon turn out to be
extremely small. We also consider the nonrelativistic limit, leading to the
familiar elementary emission model, and demonstrate the importance of
relativistic effects. It is found that the nonrelativistic approach evidently
misses sensible influences from Lorentz boosts and some essential spin-coupling
terms.Comment: 6 pages, 3 table
Covariant calculation of mesonic baryon decays
We present covariant predictions for pi and eta decay modes of N and Delta
resonances from relativistic constituent-quark models based on
one-gluon-exchange and Goldstone-boson-exchange dynamics. The results are
calculated within the point-form approach to Poincare-invariant relativistic
quantum mechanics applying a spectator-model decay operator. The direct
predictions of the constituent-quark models for covariant pi and eta decay
widths show a behaviour completely different from previous ones calculated in
nonrelativistic or so-called semirelativistic approaches. It is found that the
present theoretical results agree with experiment only in a few cases but
otherwise always remain smaller than the experimental data (as compiled by the
Particle Data Group). Possible reasons for this behaviour are discussed with
regard to the quality of both the quark-model wave functions and the mesonic
decay operator.Comment: 10 pages, 2 figures, accepted for publication in Phys. Rev.
Axial Transition Form Factors and Pion Decay of Baryon Resonances
The pion decay constants of the lowest orbitally excited states of the
nucleon and the along with the corresponding axial transition
form factors are calculated with Poincar\'e covariant constituent-quark models
with instant, point and front forms of relativistic kinematics. The model wave
functions are chosen such that the calculated electromagnetic and axial form
factors of the nucleon represent the empirical values in all three forms of
kinematics, when calculated with single-constituent currents. The pion decay
widths calculated with the three forms of kinematics are smaller than the
empirical values. Front and instant form kinematics provide a similar
description, with a slight preference for front form, while the point form
values are significantly smaller in the case of the lowest positive parity
resonances.Comment: 18 pages, 5 figures. Slightly revised, accepted in Phys. Rev.
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
Axial-vector mesons in a relativistic point-form approach
The Poincare invariant coupled-channel formalism for two-particle systems
interacting via one-particle exchange, which has been developed and applied to
vector mesons in Ref. [1] is applied to axial vector mesons. We thereby extend
the previous study of a dynamical treatment of the Goldstone-boson exchange by
comparison with the commonly used instantaneous approximation to the case of
orbital angular momentum l=1. Effects in the mass shifts show more variations
than for the vector-meson case. Results for the decay widths are sizable, but
comparison with sparse experimental data is inconclusive.Comment: 4 pages, 1 figur
Electromagnetic nucleon form factors in instant and point form
We present a study of the electromagnetic structure of the nucleons with
constituent quark models in the framework of relativistic quantum mechanics. In
particular, we address the construction of spectator-model currents in the
instant and point forms. Corresponding results for the elastic nucleon
electromagnetic form factors as well as charge radii and magnetic moments are
presented. We also compare results obtained by different realistic nucleon wave
functions stemming from alternative constituent quark models. Finally, we
discuss the theoretical uncertainties that reside in the construction of
spectator-model transition operators.Comment: 13 pages, 9 figures, updated and extended version for publicatio
The role of components in the nucleon and the N(1440) resonance
The role of components in the nucleon and the N(1440) resonance is
studied by explicit coupling of the lowest positive parity state
to the components in the harmonic oscillator quark model. The lowest
energy component, where the 4-quark subsystem has the flavor-spin
symmetry , is close in energy to the lowest positive
parity excitation of the nucleon in the quark model. The confining
interaction leads to a strong mixing of the system and the
positive parity excited state of the system. This result is in line with
the phenomenological indications for a two-component structure of the N(1440)
resonance. The presence of substantial components in the N(1440) can
bring about a reconciliation of the constituent quark model with the large
empirical decay width of the N(1440).Comment: Accepted for publication in Nucl. Phys.
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