THEORY OF EXCITATIONS IN A FERMION SYSTEM WITH LARGE QUNANTUM FLUCTUATIIONS : RESONATING HB APPROXIMATION AND RESONATING HB RPA

抄録

We develop a theory of excitations in a Fermion system with large quantum fluctuations that can be described by resonance of non-orthogonal HB wavefunctions with different correlation structures. First we will derive a new variation equation called the Resonating HB equation in order to determine the Resonating HB wavefunctions. Next, we will obtain a new approximation for excitations from time dependent small fluctuations of the Resonating HB ground state, i.e., the Resonating HB RPA. It gives two kinds of excitations. One is the collective excitations called vibrons due to secular vibrations of orbitals in the Res HB wavefunctions. The Res HB RPA gives many different classes of the vibrons arising from different HB wavefunctions involved in the ground state. Another kind of excitations arises from secular vibrations of the mixing coefficients of the Res HB wavefunctions. These new excitations called resonons are shown to correspond to the excited states in the Res HB theory due to the resonance of the HB wave functions. The Res HB RPA gives a unified description of the vibrons and resonons and their interactions.