Collective multipole excitations based on correlated realistic nucleon-nucleon interactions

Abstract

We investigate collective multipole excitations for closed shell nuclei from 16O to 208Pb using correlated realistic nucleon -nucleon interactions in the framework of the random phase approximation (RPA). The dominant short-range central and tensor correlations a re treated explicitly within the Unitary Correlation Operator Method (UCOM), which provides a phase-shift equivalent correlated interaction V_UCOM adapted to simple uncorrelated Hilbert spaces. The same unitary transformation that defines the correlated interaction is used to derive correlated transition operators. Using V_UCOM we solve the Hartree-Fock problem and employ the single-particle state s as starting point for the RPA. By construction, the UCOM-RPA is fully self-consistent, i.e. the same correlated nucleon-nucleon interact ion is used in calculations of the HF ground state and in the residual RPA interaction. Consequently, the spurious state associated with t he center-of-mass motion is properly removed and the sum-rules are exhausted within +-3%. The UCOM-RPA scheme results in a collective character of giant monopole, dipole, and quadrupole resonances in closed-shell nuclei across the nuclear chart. For the isoscalar giant monopole resonance, the resonance energies are in agreement with experiment hinting at a reasonable compressibility. However, in the 1- and 2+ channels the resonance energies are overestimated due to missing long-range correlations and three-body contributions.