有限温度RPA方程式の拡張と巨大共鳴におけるエントロピー効果(原子核動力学における散逸と減衰,研究会報告)

抄録

An extended form of the thermal random phase approximation (ETRPA) equation is derived by applying the variational principle to the grand potential. The ETRPA equation is a realization of the desirable formalism which is exact within the framework of the random phase approximation (RPA) at finite temperature (T≠0), and smoothly goes to the RPA equation in the limit of T → 0. It describes an interplay between the collective excitations and the entropy effect. The ETRPA matrix precisely cincides with the stability matrix for the thermal Hartree-Fock-Bogoliubov (THFB) solution. The entropy effect is associated with the fluctuation of the occupation numbers in each single-particle (or quasiparticle) level determined by the mean field equation (i.e. the THFB equation). Based on a simple model, it can be shown that the entropy effect causes some shifts of excitation energies of the ph, pp and hh configurations, and it may slightly affect the temperature-dependent evolution of the giant resonance shape.