Temporal nonlocality of nuclear and atomic mean fields

Abstract Microscopic theories of the nuclear and atomic mean fields lead to a potential which is nonlocal in time as well as in space. Some properties of the temporal nonlocality are examined, including the consequences of requiring that causality be satisfied. One of these consequences is that the temporal nonlocality is fully determined by the energy dependence of the imaginary part of the field. It is shown that different temporal nonlocalities are associated with the two basic microscopic definitions of the mean field, namely Feshbach's potential and the self-energy. A physical interpretation of the temporal nonlocality is presented, in terms of a time delay induced by couplings to nonelastic channels. Models for the temporal nonlocality of the nucleon-nucleus mean field are analyzed.