A new boson realization of the two-level pairing model in a many-fermion system and its classical counterpart - The role of the su(2) circle times su(1,1)-coherent state in the Schwinger boson representation for the su(2) circle times su(2)-algebra

摘要

A new method for describing the two-level pairing model in a many-fermion system is presented. The basic idea comes from the Schwinger boson representation for the su(2) x su(2)-algebra, in which four kinds of boson operators govern the dynamics. It is well known that in the original fermion space, it is almost impossible to introduce any trial state for the variation except the BCS state in the framework of the mean field approximation. However, in the Schwinger boson representation, various trial states can be defined on the condition that the mean field approximation is useful. In these states, the su(2) x su(1, 1)-coherent state is mainly discussed in this paper.