Nuclear friction and quantum mechanical diffusion

We study dissipative properties of the motion of a slow nuclear collective variable weakly coupled to a complex quantum environment formed by the fast nucleonic degrees of freedom. The fast quantum mechanical subsystem is treated within the random matrix approach, where the complexity of the nucleonic degrees of freedom's motion can be changed by a parameter from regular to fully chaotic. Classical dynamics is assumed for the slow variable, and the equation of motion is determined from conservation of the total energy of the nuclear many-body system. We show that the macroscopic equation of motion for the collective variable is subject to a memory-dependent friction force, with a retardation defined by the chaoticity of the fast nucleonic environment.