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We investigate the structure of the nucleon resonance N*(1440) ͑Roper͒ within a coupled-channel meson exchange model for pion-nucleon scattering. The coupling to N states is realized effectively by the coupling to the N, ⌬, and N channels. The interaction within and between these channels is derived from an effective Lagrangian based on a chirally symmetric Lagrangian, which is supplemented by well known terms for the coupling of the ⌬ isobar, the meson, and the '','' which is the name given here to the strong correlation of two pions in the scalar-isoscalar channel. In this model the Roper resonance can be described by meson-baryon dynamics alone; no genuine N*(1440) ͑three quark͒ resonance is needed in order to fit N phase shifts and inelasticities.

We present a complete set of formulas for longitudinal momentum distribution functions (splitting functions) of mesons in the nucleon. It can be applied in the framework of convolution formalism to the deep-inelastic structure functions (quark distributions) of the nucleon viewed as a system composed of virtual 'mesons' and 'baryons'. Pseudoscalar and vector mesons as well as octet and decuplet baryons are included. In contrast to many approaches in the literature the present approach ensures charge and momentum conservation by the construction. We present not only spin averaged splitting functions but also helicity dependent ones, which can be used to study the spin content of the nucleon. The cut-off parameters of the underlying form factors for different vertices are determined from high-energy particle production data. We find an universal cut-off parameter for processes involving octet

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The N interaction is studied within a meson-exchange model and in a coupled-channels approach which includes the channels N, N, as well as three effective N channels, namely, N, ⌬, and N. Starting out from an earlier model of the Jülich group systematic improvements in the dynamics and in some technical aspects are introduced. With the new model an excellent quantitative reproduction of the N phase shifts and inelasticity parameters in the energy region up to 1.9 GeV and for total angular momenta Jഛ3/2 is achieved. Simultaneously, good agreement with data for the total and differential N→N transition cross sections is obtained. The connection of the N dynamics in the S 11 partial wave with the reaction N→N is discussed.

η meson production in both proton-proton and proton-neutron collisions is investigated within a relativistic meson exchange model of hadronic interactions. It is found that the available cross section data can be described equally well by either the vector or pseudoscalar meson exchange mechanism for exciting the S 11 (1535) resonance. It is shown that the analyzing power data can potentially be very useful in distinguishing these two scenarios for the excitaion of the S 11 (1535) resonance.

We review an extension of Migdal's Theory of Finite Fermi Systems which has been developed and applied to collective vibrations in closed shell nuclei in the past ten years. This microscopic approach is based on a consistent use of the Green function method. Here one considers in a consistent way more complex 1p1h⊗phonon configurations beyond the RPA correlations. Moreover, these configurations are not only included in the excited states but also explicitly in the ground states of nuclei. The method has been applied to the calculation of the strength distribution and transition densities of giant electric and magnetic resonances in stable and unstable magic nuclei. Using these microscopic transition densities, cross sections for inelastic electron and alpha scattering have been calculated and compared with the available experimental data. The method also allows one to extract in a consistent way the magnitude of the strength of the various multipoles in the energy regions in which several multipoles overlap. We compare the microscopic transition densities, the strength distributions and the various multipole strengths with their values extracted phenomenologically.

A dynamical model for pseudoscalar-pseudoscalar meson scattering based on meson exchange, suitable for use in a variety of low-and intermediate-energy mesonic interactions, has been constructed and applied to rr and Krr scattering with good quantitative results. The model includes both sand t-channel exchange, and is found to require pseudoscalar-pseudoscalar coupling to a scalar octet to fit the high energy s-wave phases in the I = 0 r~ channel and in the I =f KQT channel. Coupling of the rr and KI? channels is found to play a crucial role in explaining the S*(975) resonance.