Quasi spin pairing and the structure of the Lipkin Model

Abstract

By introducing the concepts of quasi-spin pairing and quasi-spin seniority, the Lipkin model is extended to a variable number of particles. The properties of quasi-spin pairing are seen to be quite similar to those of ordinary pairing. The quasi-spin seniority allows one to obtain a simple classification of excited multiplets. A “pairing plus monopole” model is studied in connection with the Hartree-Fock theory.