Crossing symmetric scattering, or, lacing the bootstrap

The authors develop a non-perturbative approximation scheme for a generic field theory with fermion-antifermion-boson interaction, based on the Schwinger-Dyson equations. They approximate the 4-point vertex with the sum of all 2-particle reducible terms, in a crossing-symmetric way. This scheme generalizes the usual summation of ladder or bubble diagrams, thus providing for the summation of a larger subset of all diagrams