The influence of relativistic contributions to deuteron electrodisintegration is systematically studied in various kinematic regions of energy and momentum transfer. As theoretical framework the equation-of-motion and the unitarily equivalent S-matrix approaches are used. In a (p/M )-expansion, all leading order relativistic π-exchange contributions consistent with the Bonn OBEPQ model are included. In addition, static heavy meson exchange currents including boost terms, γπρ/ω-currents, and ∆-isobar contributions are considered.Sizeable effects from the various relativistic two-body contributions, mainly from π-exchange, have been found in inclusive form factors and exclusive structure functions for a variety of kinematic regions.

The influence of relativistic contributions to elastic electron deuteron scattering is studied systematically at low and intermediate momentum transfers (Q 2 ≤ 30 fm −2 ). In a (p/M )-expansion, all leading order relativistic π-exchange contributions consistent with the Bonn OBEPQ models are included. In addition, static heavy meson exchange currents including boost terms and lowest order ρπγ-currents are considered. Sizeable effects from the various relativistic two-body contributions, mainly from π-exchange, have been found in form factors, structure functions and the tensor polarization T20. Furthermore, static properties, viz. magnetic dipole and charge quadrupole moments and the mean square charge radius are evaluated.

Coherent η-meson photoproduction on the deuteron has been studied, where the emphasis is on the relative importance of two-body contributions from hadronic rescattering and electromagnetic meson exchange currents besides the impulse approximation. For the elementary photoproduction amplitude a coupled resonance model developed by Bennhold and Tanabe has been used which fits reasonably well the experimental data. The rescattering effects are treated within a coupled channel approach considering the intermediate excitation of the P11(1440), D13(1520), and S11( 1535) nucleon resonances. The hadronic interaction between nucleon and resonances is modeled by one boson exchange potentials, which we have considered both in the static approximation as well as fully retarded. The sum of all considered two-body effects results in an enhancement of the total cross section between 10 in the maximum and 25 percent closer to threshold around 680 MeV if the hadronic interaction is treated retarded. This enhancement shows up in the differential cross sections mainly at backward angles. It increases steadily from only a few percent at 0 • to more than a factor two at 180 • for a photon energy of 680 MeV. Two-body effects become also significant in certain polarization observables. Finally, no discrepancy has been found for the ratio of the isoscalar amplitude to the proton amplitude between coherent and incoherent η-photoproduction on the deuteron due to a nonvanishing complex and energy dependent phase relation.

Rescattering effects in coherent eta photoproduction on the deuteron are studied in the region of the S11(1535) resonance. For the elementary reaction mechanism on the nucleon, an effective isobar model with inclusion of resonances and Born terms is used. The resonance parameters are fixed by considering pion photoproduction only. The predicted cross sections for eta production on the proton are in satisfactory agreement with experiment without any additional parameter fitting. For the coherent eta production on the deuteron we have considered the impulse approximation taking into account the P11(1440), D13(1520), and S11(1535) resonances, rescattering, and meson exchange currents. For the rescattering mechanism a coupled channel model including the dominant S11(1535) resonance is used. A reduction of the total cross section up to about 50 % through rescattering is found. This is considered as an upper limit for the size of rescattering effects due to uncertainties in the N S11 transition potential. Other two-body effects like meson exchange currents appear to be small.

Relativistic effects and the role of heavy meson exchange in deuteron photodisintegration are studied systematically for photon energies below the pion production threshold. In a (p/M )-expansion, all leading order relativistic one-body and π-exchange as well as all static heavy meson exchange currents consistent with the Bonn OBEPQ model are included. In addition, one-and two-body boost effects have been investigated. Sizeable effects from the various two-body contributions beyond πexchange have been found in almost every observable considered, i.e., differential cross section and single polarization observables.PACS numbers: 21.45.+v, 13.40.-f, 24.70.+s, 25.20.Dc † Dedicated to Prof. J.A. Tjon on the occasion of his 60th birthday. * Supported by the Deutsche Forschungsgemeinschaft (SFB 201).