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Within the previously developed Dubna-Mainz-Taipei meson-exchange model, the singularity structure of the pi N scattering amplitudes has been investigated. For all partial waves up to F waves and c.m. energies up to W = 2 GeV, the T-matrix poles have been calculated by three different techniques: analytic continuation into the complex energy plane, speed-plot and the regularization method. For all 4-star resonances, we find a perfect agreement between the analytic continuation and the regularization method. We also find resonance poles for resonances that are not so well established, but in these cases the pole positions and residues obtained by analytic continuation can substantially differ from the results predicted by the speed-plot and regularization methods., 21 pages, 4 figures, 4 tables

A Bethe-Salpeter-Faddeev (BSF) calculation is performed for the pentaquark $��^+$ in the diquark picture of Jaffe and Wilczek in which $��^+$ is a diquark-diquark-${\bar s}$ three-body system. Nambu-Jona-Lasinio (NJL) model is used to calculate the lowest order diagrams in the two-body scatterings of ${\bar s}D$ and $D D$. With the use of coupling constants determined from the meson sector, we find that ${\bar s}D$ interaction is attractive while $DD$ interaction is repulsive, and there is no bound $\frac 12^+$ pentaquark state. A bound pentaquark $��^+$ can only be obtained with unphysically strong vector mesonic coupling constants., 4 pages, 4 figures

The Dubna-Mainz-Taipei (DMT) dynamical model for pion electromagnetic production, which describe well the existing data from threshold up to 1 GeV photon lab energy is presented and used to analyze recent data in the $��$ region . We find that within DMT model, the bare $��$ is almost spherical while the physical $��$ is oblate. The deformation is almost saturated by the pion cloud effects., 4 pages, 2 postscript figures, contr. to Int. Conf. on QCD and Hadronic Physics, Beijing from Jun 16-20, 2005

Radiative pion photoproduction in the $��(1232)$ resonance region is studied with the aim to access the $��^+(1232)$ magnetic dipole moment. We present a unitary model of the $��p \to ����N$ ($��N = ��^0 p, ��^+ n$) reactions, where the $��N$ rescattering is included in an on-shell approximation. In this model, the low energy theorem which couples the $��p \to ����N$ process in the limit of a soft final photon to the $��p \to ��N$ process is exactly satisfied. We study the sensitivity of the $��p \to ����^0 p$ process at higher values of the final photon energy to the $��^+(1232)$ magnetic dipole moment. We compare our results with existing data and give predictions for forthcoming measurements of angular and energy distributions. It is found that the photon asymmetry and a helicity cross section are particularly sensitive to the $��^+$ magnetic dipole moment., 23 pages, 18 figures

We show that recent experiment data for the ratios $E_{1^+}/M_{1^+}$ and $S_{1^+}/M_{1^+}$ can be explained in a dynamical model for electromagnetic production of pions, together with a simple scaling assumption for the bare $��^* N ��$ form factors. Within our model we find that the bare $��$ is almost spherical and the electric E2 and Coulomb C2 quadrupole excitations of the physical $��$ are nearly saturated by pion cloud contribution in $Q^2 \le 4.0 GeV^2$., 8 pages, 2 figures, to appear in the Proc. of "NSTAR2000 - The Physics of Excited Nucleons", Feb. 16-19, 2000, Jefferson Lab, USA, World Scientific, Singapore, 2000

A partial wave analysis of pion photoproduction has been obtained in the framework of fixed-t dispersion relations valid from threshold up to 500 MeV. In the resonance region we have precisely determined the electromagnetic properties of the ��(1232) resonance, in particular the E2/M1 ratio R_{EM}=(-2.5 +- 0.1) %. For pion electroproduction recent experimental data from Mainz, Bates and JLab for Q^2 up to 4.0 (GeV/c)^2 have been analyzed with two different models, an isobar model (MAID) and a dynamical model. The E2/M1 ratios extracted with these two models show, starting from a small and negative value at the real photon point, a clear tendency to cross zero, and become positive with increasing Q^2. This is a possible indication of a very slow approach toward the pQCD region. The C2/M1 ratio near the photon point is found as R_{SM}(0)=(-6.5 +- 0.5) %. At high Q^2 the absolute value of the ratio is strongly increasing, a further indication that pQCD is not yet reached., 10 pages LaTeX including 3 figures. Talk given at the XVIIth European conference on Few-Body Problems in Physics, Evora, Portugal, 11 - 16 September 2000; to be published in Nucl.Phys. A