New Factorized Off-Shell Prescription for the Distorted-Wave Impulse Approximation in Knockout Reactions

The distorted-wave impulse approximation for knockout reactions, when written following a Faddeev prescription, contains a fully off-shell $T$ matrix whose arguments are coupled to those of the distorted waves. We show how the off-shell $T$ matrix may be expanded around its half-shell point and an approximate factorized distorted-wave impulse approximation obtained with the major off-shell effect included. The off-shell ambiguity present in the standard treatments is thereby eliminated.