Three-body model of the final state interaction in heavy meson decay

We develop a relativistic three-body model for the final state interaction in D+→K−π+π+ decay based on the ladder approximation of the Bethe-Salpeter equation. The decay amplitude has the standard two-meson resonant transition matrix modulated by a spectator amplitude that carries a fully interacting three-body contribution and a smooth background term from the partonic amplitude. Our calculations are compared with D decay data.