Kazuhiko Nishijima

Many-Body Problem in Quantum Field Theory, III

In view of the fact that really observable particles are not bare but dressed with their self field, the procedures to treat rigorously the dressed particles are presented. For this purpose, the Green function formalism by Schwinger and covariant equations by Bethe and Sal peter are useful. In this paper, we first discuss the relations among various covariant formulations. Then it is investigated how to normalize the Bethe-Salpeter wave functions and how to exp~ess the expectation values of given observables· in terms of Bethe-Salpeter wave functions. Finally the difference of treatments between dressed and bare particles are shown in connection with the scattering problems.

ON THE INTERACTION BETWEEN HYPERONS AND NUCLEONS AND THE HYPERFRAGMENTS

Based on the principle of charge independence and the experimentally established evidences for the existence of the hyperfragment 3H*, the nature of the force between a A0 particle and a nucleon is investigated. It is shown that the range of the A-N force cannot be longer than half the pion Compton wave length and that its well depth parameter is larger than about 0.4. This result suggests us the possible existence of the so-called hyper di-nucleons. Next, the mechanism of the non-mesonic to decays of a hyperfragment 4He* is investigated. A qualitative argument leads to the conclusion that the spin of the A0 particle cannot be larger than 3/2.