Hole spectral functions and collective excitations

Abstract

Proton-hole spectral functions are calculated by solving the Dyson equation for the one-body Green function using a realistic G-matrix interaction. The consequences of replacing non-interacting intermediate states in the second-order self-energy by interacting ones is studied. These interactions are treated in Tamm-Dancoff approximation (TDA) as well as in random-phase approximation (RPA) for particle-hole or particle-particle (hole-hole) correlations. The influence of these correlations is illustrated for the spectral-strength distributions in 48Ca and 90Zr. The influence of a more realistic treatment of the states to which the particles couple is particularly strong at low energy, where such coherence phenomena are most important and where they yield additional fragmentation of single-particle strength. In accord with this observation, an increased depletion of mostly filled shells just below the Fermi energy and an increased occupation of mostly empty shells just above the Fermi energy is obtained. Instabilities found in the RPA treatment, point to the need of a self-consistent approach. Comparison with recent (e,e′p) data yields an estimate of about 10–15% for the amount of strength that is depleted by short-range correlations.