Theory of dressed n-quasi particle (nQP) modes

Concept of the dressed n-quasi particle state is introduced and discussed for the study of nuclear excited states. In chapter 1, a method is described which was developed to separate the spurious components from the quasi-particle states, and to keep precisely the one-to-one correspondence between the senority number and the quasi particle number. The detailed formal structure of the dressed n-quasi particle (nQP) modes is studied in chapter 2. In order to specify the modes in the ''intrinsic'' space, it is decisive to use the concept of spherical tensor in the quasi-spin space. It is necessary to find a method of transcription of the physical operators in the quasi-particle Tamm-Dancoff space into the quasi-particle new Tamm-Dancoff space. Detail of the method is also discussed in chapter 2. In chapters 3 and 4, recent experimental results are shown, which revealed the systematic presence of this new kind of collective mode in spherical odd-mass nuclei. The subject of chapter 5 is the investigation of the microscopic structure of the breaking and persistency of the conventional ''phonon-plus-odd-quasi-particle picture''. Comparison between the results with the pairing plus quadrupole force and the more complex residual force is presented in chapter 6. The formal structure and the physical implication of coupling between pairing mode and dressed nQP mode is described in chapter 7. (Kato, T.)