Beyond the Schwinger boson representation of the su(2)-algebra. I -- New   boson representation based on the su(1,1)-algebra and its related problems   with application
  With the use of two kinds of boson operators, a new boson representation of the su(2)-algebra is proposed. The basic idea comes from the pseudo su(1,1)-algebra recently given by the present authors. It forms a striking contrast to the Schwinger boson representation of the su(2)-algebra which is also based on two kinds of bosons. This representation may be suitable for describing time-dependence of the system interacting with the external environment in the framework of the thermo field dynamics formalism, i.e., the phase space doubling. Further, several deformations related to the su(2)-algebra in this boson representation are discussed. On the basis of these deformed algebra, various types of time-evolution of a simple boson system are investigated. 
Yasuhiko Tsue (Kochi Univ., Japan), Constanca Providencia (Univ. de   Coimbra, Portugal), Joao da Providencia (Univ. de Coim...
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