Gauge-invariant models for two-body scattering with the Bethe-Salpeter ladder approximation

A natural and self-consistent method is given in the context of the ladder approximation of the Bethe-Salpeter equation for the construction of gauge-invariant models for two-body scattering involving photons. One vertex in these models is assumed to have structure and to be described by a Bethe-Salpeter equation. As examples, models for the following reactions are given: γN->γN; γN->π±,⁰N, ρ±,⁰N; γπ->γπ; γπ->ρ±,⁰π.