The (pi+,pi-) double-charge-exchange reaction for pion energies of 200 to 1400 MeV is calculated with a zero-parameter Glauber theory that includes spin flip and pion absorption. Differential cross sections and excitation functions are obtained for C-14 and O-18 targets. Results for T(pi)=300-525 MeV are compared with recent experimental results and suggest a new quenching process. We have calculated effects of medium polarization on the isovector pion operator and find a strong reduction in good agreement with data. A pronounced dip in the cross section near T(pi)=1300 MeV offers a unique testing ground for unconventional mechanisms.

We have evaluated the mechanism analogous to pion absorption which contributes to the pion double-charge-exchange amplitude leading to double isobar analog states. We find appreciable corrections at low energies around T(pi) = 50 MeV. Around the resonance region the corrections are small and the most visible effect is a small shift of the minimum to smaller angles, which is however not big enough to reproduce the experimental data.

The s-wave meson-baryon interaction in the S=-1, S=0 and S=-2 sectors is studied by means of coupled channels, using the lowest-order chiral Lagrangian and the N/D method or equivalently the Bethe-Salpeter equation to implement unitarity. This chiral approach leads to the dynamical generation of the Lambda(1405), Lambda(1670) and Sigma(1620) states for S=-1, the N*(1535) for S=0 and the Xi(1620) for S=-2. We look for poles in the complex plane and extract the couplings of the resonances to the different final states. This allows identifying the Lambda(1405) and the Lambda(1670) resonances with KmacrN and KXi quasibound states, respectively. Our results are found to be incompatible with the measured properties of the Xi(1690) resonance, thus ruling this state out as the remaining member of this octet of dynamically generated resonances. We therefore assign 1/2 - for the spin and parity of the Xi(1620) resonance as the S=-2 member of the lowest-lying 1/2 - octet

We have investigated the mechanisms leading to two and three body photon absorption in nuclei. At photon energies around the pion production threshold we obtain a fraction of three body absorption of less than 10% of the total, contradicting previous theoretical claims that it dominates the absorption process. The strength of the three body channel grows smoothly with the photon energy reaching a maximum of about 60% of the total direct absorption at energies of the photon around 400 MeV.

We study pion-induced single- and double-charge exchange reactions in nuclei at energies above the DELTA(3/2, 3/2) resonance using a microscopic, parameter-free Glauber approach. We introduce corrections in the amplitudes due to the medium polarization from an isospin-flip spin-nonflip source which dominates the reaction in the transitions studied and which has not previously been identified. Using an effective force derived from the study of electromagnetic transitions we obtained sizable reductions of the cross sections in both single- and double-charge exchanges, which bring the results of both reactions into close agreement with experiment. Predictions for angular distributions for both reactions on C-14 O-18, and Ca-42 targets are made which should serve as guidelines for experiments planned in this region and as further tests of the proposed isovector renormalization.