The Lipkin Model in Many-Fermion System as an Example of the su(1,1)   times su(1,1)-Algebraic Model
  Following the idea, recently, proposed by the present authors for the two-level pairing model, the Lipkin model is reexamined. It is a natural generalization of the method already developed by the present authors with Kuriyama. This model is a schematic model for many-fermion system and obeys the su(2)-algebra. It is shown that the use of the Schwinger boson representation, the model is expressed in terms of the su(1,1) times su(1,1)-algebra and with the aid of the MYT mapping method, it is disguised from the orginal form in terms of the Holstein-Primakoff representation. Further, under various coherent states, the classical counterparts are derived. It is concluded that the Lipkin model can be treated in the common ring as that of the two-level pairing model. 
C. Providencia (Univ. de Coimbra, Portugal), J. da Providencia (Univ.   de Coimbra, Portugal), Y. Tsue (Kochi Univ., Japan),...