Effects of nuclear fragmentation on single particle and collective motions at low energy
The Faddeev technique is employed to study the influence of both particle-particle and particle-hole phonons on the one-hole spectral function of 16O. The formalism includes the effects of nuclear fragmentation and accounts for collective excitations at a random phase approximation (RPA) level. The latter are subsequently summed to all orders by the Faddeev equations to obtain the nucleon self-energy. The results indicate that the characteristics of hole fragmentation are related to the low-lying states of 16O and an improvement of the description of this spectrum is required to understand the details of the experimental strength distribution. A first calculation to improve on this includes the mixing of two-phonon configuration with particle-hole ones. It is seen that this allows to understand the formation of excited states which cannot be described by the RPA approach.