Giant Resonances using the UCOM and Second RPA

We aim to describe nuclear collective excitations starting from correlated realistic nucleon-nucleon (NN) interactions. The latter are constructed within the Unitary Correlation Operator Method (UCOM) [1, 2], which explicitly considers short-range correlations in order to properly soften the short-range behaviour of realistic NN potentials. It has been concluded that first-order RPA with a two-body UCOM interaction (UCOM-RPA) is not capable, in general, of reproducing quantitatively the properties of giant resonances (GRs), due to missing higher-order configurations and long-range correlations as well as neglected three-body terms in the Hamiltonian [3, 4]. In this work we go beyond first-order RPA and employ a UCOM interaction, VUCOM, in Second RPA (SRPA) [5, 6]. The coupling between ph and 2p2h excitations is taken into account. Excitations are built on top of the Hartree-Fock (HF) ground state, as in the usual RPA. The same interaction is used to describe the Hartree-Fock (HF) ground state and the residual interactions. The HF-based formulation of SRPA preserves the sum rules m0 and m1 of RPA [5], but not symmetries like translational invariance [7]. We have used the correlated Argonne V18 interaction and we have examined the IS monopole (ISM), IV dipole (IVD) and IS quadrupole (ISQ) response of the nuclei O and Ca. We present our results in comparison with experimental data in Fig.1. In all cases, the SRPA centroid