On the occurrence of dissipative forces in the scattering of two heavy ions

Starting with a semi-microscopic model for the quantum description of colliding ions the authors deduce an effective classical equation for the relative motion in which the coupling between the relative motion and the intrinsic nucleonic degrees of freedom appears implicitly as dissipative and conservative forces. In their formulation the authors distinguish between processes (non-collective excitations) which have a short relaxation time and processes (low-lying collective excitations) which relaxation time is of the order of the collision time. In the first case a frictional-like term appears in the effective equation of motion while in the second case effective force becomes nonlocal in time. A rigorous formulation of the problem in the Zubarev formalism is also given