1,162 research outputs found
Electromagnetic Couplings of Nucleon Resonances
An effective Lagrangian calculation of pion photoproduction including all
nucleon resonances up to GeV is presented. We compare our
results to recent calculations and show the influence of different width
parametrizations and offshell cutoffs on the photoproduction multipoles. We
determine the electromagnetic couplings of the resonances from a new fit to the
multipole data.Comment: 20 pages, latex, 6 figures. Misprints corrected, text & 3 figures
adde
Couplings varying on cosmological scales and Lorentz breaking
In the context of N=4 supergravity in four dimensions, we present an exact
classical solution that leads to spacetime-dependent electromagnetic couplings
and discuss the ensuing Lorentz-violating effects. We comment briefly on
experimental bounds.Comment: 10 pages, 1 figure, invited talk presented at the Coral Gables
Meeting, December 200
Electromagnetic couplings in a collective model of the nucleon
We study the electromagnetic properties of the nucleon and its excitations in
a collective model. In the ensuing algebraic treatment all results for helicity
amplitudes and form factors can be derived in closed form in the limit of a
large model space. We discuss nucleon form factors and transverse
electromagnetic couplings in photo- and electroproduction, including transition
form factors that can be measured at new electron facilities.Comment: latex, 12 pages, 5 figures uuencoded. Invited talk at the XVIII
Nuclear Physics Symposium at Oaxtepec, to be published in Revista Mexicana de
Fisic
Algebraic models of hadron structure: I. Nonstrange baryons
We introduce an algebraic framework for the description of baryons. Within
this framework we study a collective string-like model and show that this model
gives a good overall description of the presently available data. We discuss in
particular masses and electromagnetic couplings, including the transition form
factors that can be measured at new electron facilities.Comment: to be published in Annals of Physics (N.Y.), 44 pages of LaTex, 11
postscript figure files on request, UU-94-0
Scale dependent three-dimensional charged black holes in linear and non-linear electrodynamics
In the present work we study the scale dependence at the level of the
effective action of charged black holes in Einstein-Maxwell as well as in
Einstein-power-Maxwell theories in (2+1)-dimensional spacetimes without a
cosmological constant. We allow for scale dependence of the gravitational and
electromagnetic couplings, and we solve the corresponding generalized field
equations imposing the "null energy condition". Certain properties, such as
horizon structure and thermodynamics, are discussed in detail.Comment: v1: 13 pages, 10 figure
Hybrid Baryon Signatures
We discuss whether a low-lying hybrid baryon should be defined as a three
quark - gluon bound state or as three quarks moving on an excited adiabatic
potential. We show that the latter definition becomes exact, not only for very
heavy quarks, but also for specific dynamics. We review the literature on the
signatures of hybrid baryons, with specific reference to strong hadronic
decays, electromagnetic couplings, diffractive production and production in psi
decay.Comment: Talk at ``The Physics of Excited Nucleons'' (NSTAR2000), Newport
News, VA, 16-19 Feb. 2000. 8 pages, LaTe
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