Second Random Phase Approximation with Skyrme Interaction

11h -seminar room GANIL (105)

a coffee will be served 15 mn before

The Second Random Phase Approximation (SRPA) is a natural extension of RPA obtained by introducing more general excitation operators where two particle-two hole configurations, in addition to the one particle-one hole ones, are considered. First, some formal properties of SRPA are presented and then, some applications of Skyrme-SRPA to ¹⁶O
are shown. Current versions of SRPA are almost always based on non-interacting two particle-two hole configurations. This means that only the coupling between two particle-two hole and one particle-one hole
configurations is taken into account, in the so-called "diagonal" approximation. The quality of this approximation is studied comparing it with the full SRPA results. The issue of the rearrangement terms in thematrix elements beyond the standard RPA, when density-dependent force are used, is discussed and  two different approximated, and  often used, schemes are tested: the rearrangement terms are either neglected or evaluated with the RPA procedure. As a general feature of SRPA results, a several-MeV shift of the strength distribution to lower energies is systematically found with respect to RPA. A much more important fragmentation of the strength is also naturally provided by SRPA due to the huge number of two particle-two hole configurations. Finally, a better description of the excitation energies of the low-lying 0⁺ and 2⁺ states is also obtained and discussed.