Dissipation Mechanism of the Large-Amplitude Collective Motion: Dynamical Evolution of a Collective Budle of Trajectories in the TDHF Phase Space for a Simple Soluble Model

A new microscopic origin responsible for the dissipation process of the large-amplitude collective motion is discussed in terms of the dynamics of distribution function in the time-dependent Hartree Fock (TDHF) phase space. With the use of a simple soluble model, the origin is illustrated by numerically solving the master equation in the microscopic theory of nuclear collective dynamics which has been proposed by the present authors aiming at studying the order-to-chaos transitions of the large-amplitude nuclear collective motion. In this framework, collectivity of the system is expressed by a bundle of trajectories in the TDHF phase space and the dissipation process is related to the diffusive property of the bundle of trajectories. It is clarified that the microscopic dynamics responsible for the dissipation process originates from the dynamical fluctuation part of the coupling between the collective (relevant) and intrinsic (irrelevant) degrees of freedom.