Reduction of the many-body problem and the unified theory for nuclear reaction

We reduce the many-body problem to a multi-channel few-body problem by the AGS method. The channels may be chosen according to the problem under consi deration and the reduction is formally exact. For the nuclear reaction we m ay choose some one-body channels to represent compound nucleus and choose s ome two- or more-body channels to represent open reaction channels. We then apply formal collision theory to this multi-channel system. Direct reactio n, resonant reaction and their interference emerge. There are also distorti ons of ingoing and outgoing waves in compound nucleus formation and decay r espectively. The omission of all but one open channel leads to the optical model, and an incomplete consideration of the open channels may lead to a m ulti-channel generalization of the optical model. Nonnucleon degrees of fre edom as well as relativity may be included in principle. The reaction induc ed by particles other than nuclei may be considered on the same footing.