Time-dependent optical potentials: non-Markovian and doorway approaches

The authors propose new approximations to the time-dependent optical potential coupling that part of the Hilbert space in which standard truncated close coupling equations are solved (P space) and the complementary Q space. They define a dynamical basis in P space allowing for a transparent separation of P-Q and Q-Q coupling from P-P coupling, thus ensuring that account for the latter exactly within any approximate scheme. Studying the time structure of the evolution operator in Q space, they are led to propose a non-Markovian scheme going beyond the instantaneous approximation. Alternatively, a topological study of the coupling between P and Q space leads to a doorway space approximation consisting in a dynamical extension of the P space by that part of the Q space to which it is directly coupled.