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Recent progress on the extraction of electromagnetic properties of nucleon resonance excitation through pion photo- and electroproduction is reviewed. Cross section data measured at MAMI, ELSA, and CEBAF are analyzed and compared to the analysis of other groups. On this basis, we derive longitudinal and transverse transition form factors for most of the four-star nucleon resonances. Furthermore, we discuss how the transition form factors can be used to obtain empirical transverse charge densities. Contour plots of the thus derived densities are shown for the Delta, Roper, S11, and D13 nucleon resonances.
We use the Nambu-Jona-Lasinio model as an effective quark theory to investigate the medium modifications of the nucleon electromagnetic form factors. By using the equation of state of nuclear matter derived in this model, we discuss the results based
We show that two almost degenerate poles near the $piDelta$ threshold and the next higher mass pole in the $P_{11}$ partial wave of $pi N$ scattering evolve from a single bare state through its coupling with $pi N$, $eta N$ and $pipi N$ reaction chan
A dressed-quark core contribution to nucleon electromagnetic form factors is calculated. It is defined by the solution of a Poincare covariant Faddeev equation in which dressed-quarks provide the elementary degree of freedom and correlations between
Longitudinal and transverse transition form factors for most of the four-star nucleon resonances have been obtained from high-quality cross section data and polarization observables measured at MAMI, ELSA, BATES, GRAAL and CEBAF. As an application, w
We look for $DeltaDelta$ and $NDelta$ resonances by calculating $NN$ scattering phase shifts of two interacting baryon clusters of quarks with explicit coupling to these dibaryon channels. Two phenomenological nonrelativistic chiral quark models givi