THE EXTENDED TREE-LEVEL MODEL FOR THE PION-NUCLEON INTERACTION

The recently proposed model for the pion-nucleon interaction, based on sigma, rho, N and DELTA-isobar exchanges, is investigated further. We demonstrate the validity of the unitarity prescription. We prove that the inclusion of the higher resonances has a very small effect, only on the parameters of the model. The coupling constants g(piNN) and g(p iNDELTA), as deduced with the model, are found to be very close to the literature values. This is interpreted as an indication that the mode l should provide an excellent description of the pion-nucleon interact ion at low energies. Our prediction for the piNSIGMA-term is found to be independent of the only free parameter of our model (G(rho)(V)). A number of applications, both for the pion-nucleon and pion-nucleus int eractions, are discussed.