The energy dependence of the $πN$ amplitude and the three-nucleon interaction

Abstract

By calculating the contribution of the $π-π$ three-body force to the three-nucleon binding energy in terms of the $πN$ amplitude using perturbation theory, we are able to determine the importance of the energy dependence and the contribution of the different partial waves of the $πN$ amplitude to the three-nucleon force. A separable representation of the non-pole $πN$ amplitude allows us to write the three-nucleon force in terms of the amplitude for $NN\rightarrow NN^*$, propagation of the $NNN^*$ system, and the amplitude for $NN^*\rightarrow NN$, with $N^*$ being the $πN$ quasi-particle amplitude in a given state. The division of the $πN$ amplitude into a pole and non-pole gives a procedure for the determination of the $πNN$ form factor within the model. The total contribution of the three-body force to the binding energy of the triton for the separable approximation to the Paris nucleon-nucleon potential (PEST) is found to be very small mainly as a result of the energy dependence of the $πN$ amplitude, the cancellation between the $S$- and $P$-wave $πN$ amplitudes, and the soft $πNN$ form factor.