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We calculate the electromagnetic form factors of the Λ 0 and ∑ 0 hyperons using a relativised constituent quark model which includes correction terms related to the potential acting between the quarks and to the center-of-mass motion during the photon-baryon scattering. Effects of the broken SU(3) symmetry on the charge distribution inside the baryon are analysed by comparing the results to the nucleonic case. Magnetic transition moments and decay widths are calculated for the most important hyperon resonances.

In this paper, we present numerical results for electroproduction amplitudes of proton resonances and electromagnetic nucleon form factors calculated in a relativized quark model. Interactions with both transversely and longitudinally polarized virtual photons were considered. Contributions of the different effects included in our approach have been analysed through a sample comparison with the available data. We also discuss the validity of the usual single-quark transition ansatz and possible parametrizations of the potential acting between the constituent quarks of the baryon. Impressive agreement is obtained with the nucleon form factor data up to squared momentum transfers of 2.5 GeV2, but still some problems remain with the Δ(1232) and higher resonances.

We study the current-algebra approach to the Gerasimov-Drell-Hearn sum rule, paying particular attention to the infinite-momentum limit. Employing the order-alpha^2 Weinberg-Salam model of weak interactions as a testing ground, we find that the legitimacy of the infinite-momentum limit is intimately connected with the validity of the naive equal-times algebra of electric charge densities. Our results considerably reduce the reliability of a recently proposed modification of the Gerasimov-Drell-Hearn sum rule, originating from an anomalous charge-density algebra., 12 pages; 6 figures; LaTeX; submitted to Z.Phys.C

In the history of Elementary Particle Physics quite a few experimental results aroused the interest of a broader Physics community. This time experiments with polarized electron and muon beams on polarized proton targets gave rise to excitements leading to headlines like [1] “The Proton Spin Crisis — Where, oh where is the proton spin?” There are good reasons for such an excitement since basically one experimental number — see equation (1) below ! — has put a big question mark to our understanding of the structure of the most abundant and important hadron: the proton. Therefore this year at each Particle or Nuclear Physics Conference reviews on the “Proton Spin Problem” are given and especially at this Symposium on High Energy Spin Physics it is a most appropriate topic.

The predictions of reggeized vector meson exchange in γp→pπo are discussed. For t small, the calculated ω- exchange agrees with available data. The theoretical minimum at t = -0.6 (GeV/c)2 is tentatively removed at 2 GeV by a resonant background.

Renormalization of gauge theories.- Unified models of electromagnetic and weak interactions.- Osterwalder-Schrader positivity in conformal invariant quantum field theory.- Quantum gravity.- Quantum field theory and statistical mechanics.- Critical phenomena and the renormalization group.- Renormalization group solution of Ising spin models.- Covariant parton model.- Quark confinement in gauge theories of strong interactions.- Parton models for weak and electromagnetic interactions.- The relativistic string.- Fermi - bose - supersymmetry.- Strings, conductive and otherwise.- Hadron physics at ISR energies.- Review of results obtained at the cern intersecting storage rings.

In these lectures I shall describe the progress of our understanding of the photon hadron interaction in the resonance region. I will address myself to the fundamental properties of the electromagnetic hadron current and its behaviour under symmetries as well as to a detailed description of photon couplings of hadronic states. The progress to date is based on an impressive accumulation of experimental information about photon hadron processes and its phenomenological interpretation and has led to a remarkable improvement of our insight in the electromagnetic structures of hadrons.