Property of many-phonon norm matrix

It is shown that the many-phonon states built up from collective quasiparticle pairs satisfy the orthogonality condition in a good approximation, if the approximation scheme recently proposed by Holzwarth, Janssen and Jolos is applied to the intrinsic space in the quasiparticle state space, which is orthogonal to the pairing rotational and vibrational excitations. (author)