1990 年 81 巻 6 号 p. F162-F167
It is shown that application of the thermo field dynamics to the thermal Hartree-Fock-Bogoliubov (THFB) approximation leads to the extended form of the Bloch-Messiah theorem for the finite temperature formalism. The generalized Bogoliubov transformation is brought to the canonical form on the enlarged operator space including tilded operators, and newly defined single-particle density matrix and pair tensor take into account the thermal fluctuation effect of Fermion number.