276 research outputs found
Comment on ``Relativistic cluster dynamics of nucleons and mesons. II. Formalism and examples''
In a recent paper [Phys.\ Rev.\ C{\bf 49}, 2142 (1994)], Haberzettl presented
cluster N-body equations for arbitrarily large systems of nucleons and mesons.
Application to the three-nucleon system is claimed to yield a new kind of
three-nucleon force. We demonstrate that these three-nucleon equations contain
double counting.Comment: 6 pages in Revtex 3.0, 6 Postscript figures. Accepted for publication
in Phys. Rev.
Dressing the electromagnetic nucleon current
A field-theory-based approach to pion photoproduction off the nucleon is used
to derive a microscopically consistent formulation of the fully dressed
electromagnetic nucleon current in an effective Lagrangian formalism. It is
shown how the rigorous implementation of local gauge invariance at all levels
of the reaction dynamics provides equations that lend themselves to practically
manageable truncations of the underlying nonlinearities of the problem. The
requirement of consistency also suggests a novel way of treating the pion
photoproduction problem. Guided by a phenomenological implementation of gauge
invariance for the truncated equations that has proved successful for pion
photoproduction, an expression for the fully dressed nucleon current is given
that satisfies the Ward-Takahashi identity for a fully dressed nucleon
propagator as a matter of course. Possible applications include meson photo-
and electroproduction processes, bremsstrahlung, Compton scattering, and
processes off nucleons.Comment: 10 pages, 9 figure
Analyzing eta' photoproduction data on the proton at energies of 1.5--2.3 GeV
The recent high-precision data for the reaction at
photon energies in the range 1.5--2.3 GeV obtained by the CLAS collaboration at
the Jefferson Laboratory have been analyzed within an extended version of the
photoproduction model developed previously by the authors based on a
relativistic meson-exchange model of hadronic interactions [Phys. Rev. C
\textbf{69}, 065212 (2004)]. The photoproduction can be described quite
well over the entire energy range of available data by considering ,
, , and resonances, in addition to the -channel
mesonic currents. The observed angular distribution is due to the interference
between the -channel and the nucleon - and -channel resonance
contributions. The resonances are required to reproduce some of the
details of the measured angular distribution. For the resonances considered,
our analysis yields mass values compatible with those advocated by the Particle
Data Group. We emphasize, however, that cross-section data alone are unable to
pin down the resonance parameters and it is shown that the beam and/or target
asymmetries impose more stringent constraints on these parameter values. It is
found that the nucleonic current is relatively small and that the
coupling constant is not expected to be much larger than 2.Comment: Revised version based on revised (finalized) CLAS data (14 pages, 10
figures, RevTeX4
Preserving the gauge invariance of meson production currents in the presence of explicit final-state interactions
A comprehensive formalism is developed to preserve the gauge invariance of
currents describing the photo- or electroproduction of mesons off the nucleon
when the final-state interactions of mesons and nucleons is taken into account
explicitly. Replacing exchange currents by auxiliary currents, it is found that
all contributions due to explicit final-state interactions are purely
transverse and do not contain a Kroll-Ruderman-type contact current. The
relation of the present formulation to tree-level-type prescriptions is shown.Comment: 6 pages, 2 figures; published versio
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