THE DELTA-EXCITATION ON THE SHELL-MODEL EFFECTIVE NUCLEON-NUCLEON INTERACTIONS

We have calculated the Delta particle-nucleon hole core polarization d iagram G(pp Delta h) to investigate the effect of the Delta three-nucl eon force on the shell-model effective interactions. A realistic NN <- > N Delta transition G-matrix G(N Delta) is derived using a Delta-subt racted Paris potential and the coupled-channel approach of Lee and Mat suyama. The core-polarization diagrams G(pp Delta h), second order in G(N Delta), are found to be very small for the sd-shell valence nucleo ns. Satisfactory convergence is reached by including Delta excitations up to 20 oscillator shells for the summation of the Delta intermediat e states in G(pp Delta h).