Canonical-ensemble approach to condensed boson systems

The author illustrates how a condensed boson system may be treated in the framework of the canonical ensemble retaining the condensate operators as operators. It is easy to obtain from this method the results of what one might call the modified grand canonical ensemble in which one has a fixed μ and replaces the condensate operators by the c-number N0sup(1/2). The grand canonical ensemble in which one would retain the condensate operators as operators with a fixed μ is not appropriate for a condensed boson system. The proposed method of condensed boson many-body theory is on the same mathematical footing as that of a normal many-bpdy theory. So one can apply those formulae known hitherto only for normal systems to a condensed boson system without any modification. (Auth.)