Rearrangement Collisions

We discuss the quantum-mechanical theory of rearrangement collisions. In particular, we consider: (a) the transformation of the state vector from the original basis to the basis of the rearranged system; (b) the conditions for the equivalence of the "post" and "prior" interactions when computing matrix elements; and, (c) the extension of Schwinger's variational principle to rearrangement collisions.