Method for scattering equations

A method is proposed for calculating fully off-shell t matrix elements which are solutions of Lippmann-Schwinger-type equations. This is a generalization of the Kowalski version of the Sasakawa theory of scattering. The method relies on the Fredholm reduction of an integral equation whose kernel has a singularity at a fixed point. The method yields a t matrix which satisfies the conditions of on-shell unitarity and can be readily generalized to the case of multichannel scattering problems