We investigate the role of the effective nucleon-nucleon interaction in the description of giant dipole resonances in hot nuclei. For this purpose we calculate the response function of hot nuclear matter to a small isovector external perturbation using various effective Skyrme interactions. We find that for Skyrme forces with an effective mass close to unity an undamped zero sound mode occurs at zero temperature. This mode gives rise in finite nuclei (calculated via the Steinwedel-Jenssen model) to a resonance whose energy agrees with the observed value. We find that zero sound disappears at a temperature of a few MeV, leaving only a broad peak in the dipole strength.For Skyrme forces with a small value of the effective mass (0.4-0.5), there is no zero sound at zero temperature but only a weak peak located too high in energy. The strength distribution in this case is nearly independent of temperature and shows small collective effects. The relevance of these results for the saturation of photon multiplicities observed in recent experiments is pointed out.

We study the radiative decays of J π = 3 2 + baryons in the framework of the SU(3) collective approach to the Skyrme model. We present the predictions for the decay widths and the corresponding E2/M1 ratios. We find that all considered ratios are negative and of the order of a few percent only. We discuss the effects of flavor symmetry breaking and compare our results to those obtained in related models.PACS: 11.10Lm, 12.39Dc, 13.40HqKeywords: Skyrmion, Collective quantization, Radiative hyperon decays, E2/M1 ratios.---- † Supported by the Deutsche Forschungsgemeinschaft (DFG) under contract Re 856/2-2.

We investigate the time evolution of a quark-antiquark plasma by solving numerically the relativistic transport equations derived on the Hartree level from the Nambu -Jona-Lasinio model. We find that the phase transition in the expanding quark-antiquark plasma is different as compared to that in a static plasma. The expansion competes with the transition, and finally quark droplets will be formed which subsequently hadronize.These findings raise the question of whether static thermal models can make at all any prediction about signals of that transition.

Within the Nambu{Jona{Lasinio model strange degrees of freedom are incorporated into the soliton picture using the collective approach of Yabu and Ando. The form factors of the nucleon associated with the nonet vector current are extracted. The numerical results provide limits for the strange magnetic moment: 00:05 s 0:25. For the strange magnetic form factor of the nucleon the valence quark and vacuum contributions add coherently while there are signi cant cancellations for the strange electric form factor. |||||| y Supported by the Deutsche Forschungsgemeinschaft (DFG) under contract number Re{856/2-2. z Supported by a Habilitanden scholarship of the DFG.

In the framework of the product ansatz as an approximation for the two-baryon system we review in details the derivation of the isoscalar nucleon-nucleon spin orbit potential coming from the sixth order term of the extended Skyrme model. We show that the sixth order term contributes with a positive sign, as is the case for the Skyrme term, contrary to the claims of Riska and Schwesinger. Those authors considered only one part of the force due to the sixth order term and omitted the second part which turns out to be the dominant one. Our result is independent of the parameters of the model. PACS: 11.10Lm, 12.39Dc, 13.75Cs.