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Kaon photoproduction on He3, gamma + He3 --> K+ + Hypertriton, is studied in the framework of the impulse approximation. Realistic He3 wave functions obtained as solutions of Faddeev equations with the Reid soft-core potential are used along with different Hypertriton wave functions. Results are compared for several elementary operator models, which can successfully describe the elementary kaon production off the proton up to a photon lab energy of k = 2.2 GeV. It is found that the corresponding cross sections are small, of the order of several nanobarns. It is also shown that the influence of Fermi motion is important, while the effect of different off-shell assumptions on the cross section is not too significant., 39 pages in RevTeX including 8 Postscript figures. Replaced with the version accepted in Nucl. Phys. A

We give predictions for the partial wave amplitudes of pion photoproduction near threshold by means of dispersion relations at fixed t. The free parameters of this approach are determined by a fit to experimental data in the energy range 160 MeV $\le E_{\gamma} \le$ 420 MeV. The observables near threshold are found to be rather sensitive to the amplitudes in the resonance region, in particular to the $\Delta$ (1232) and $N^*$ (1440). We obtain a good agreement with the existing threshold data for both charged and neutral pion production. Our predictions also agree well with the results of chiral perturbation theory, except for neutral pion production off the neutron., Comment: 16 pages LATEX including 4 postscript figures

The contribution of intermediate nucleon isobars to proton-proton bremsstrahlung is calculated in a relativistic model. Using conventional coupling constants and form factors for the exchange of π - and ρ-mesons we find that for photon energies ω > 100 MeV isobar excitation increases the cross section markedly over the prediction of soft-photon calculations. Our results agree well with recent experiments at incident proton energy T lab =730 MeV.

We have calculated coincidence cross sections for coherent pion electroproduction on 3He and 3H using Faddeev wave functions obtained with the Reid soft-core potential. The four coincidence structure functions, corresponding to unpolarized and polarized transverse, interference and longitudinal terms differ substantially in their energy dependence. Effects of Fermi motion and off-shell ambiguities are more pronounced for virtual than for real photons. The correct treatment of Fermi motion in the production operator decreases the maximum transverse cross section by up to 50% and lowers the peak energy by up to 50 MeV. Ratios of coherent pion production on 3He and 3H differ significantly for the four structure functions. Finally, the theoretical calculations have been compared with existing experimental data on inclusive pion electroproduction.

The reaction 3 He(γ, π + ) 3 H is studied in the impulse approximation using realistic wave functions for photon energies up to 5 MeV above threshold. The calculation is performed with Blomqvist-Laget amplitudes and Fermi motion is taken into account. At threshold we obtain the reduced cross section a( 3 He ) = 120 μb , which is in good agreement with the recent experiment of Argan et al .

We examine the applicability of the virtual photon spectrum to pion production experiments by using an exact calculation of pion electroproduction from the proton and from 3He. After deriving a new virtual spectrum formula which takes into account the recoil of light target nuclei and the proper electron kinematics near the endpoint, we find that the concept of a virtual photon spectrum in such experiments is very good.

The validity of the virtual photon concept in the analysis of deuteron electrodisintegration for equivalent photon energies up to 300 MeV is investigated. The deuteron and the final state interaction are described by the consistent nonrelativistic calculation of Fabian and Arenhoevel neglecting the effects of meson exchange currents and isobar configurations. We find that in well defined kinematic domains the use of the virtual photon concept is justified in extracting photodisintegration cross sections.

Threshold pion photoproduction has been calculated for the nucleon, within the framework of chiral bag models. The results of low-energy theorems (LET) are recovered only by taking account of Lorentz ivariance and center-of-mass (CM) correlations of the composite system. In particular the static bag model describes only the Kroll-Ruderman term of the amplitude. The suppression of spurious CM excitations by the concept of effective charges and the use of properly boosted wave functions are necessary in order to obtain also the higher-order contributions as predicted by LET.