Consistency and the exorcism of ghosts

Undesirable properties, such as ghosts, may appear if dynamic interactions are used in a Green-function description of many-body systems. This is explicitly demonstrated for interparticle interactions induced by propagating phonons. It is shown, however, that the undesirable solutions are eliminated through the proper inclusion of self-energy insertions in a consistent manner. Results of a nuclear structure calculation of the negative parity states of 18O are presented as a numerical illustration. (Auth.)