Feynman versus Bakamjian-Thomas in light-front dynamics

We compare the Bakamjian-Thomas (BT) formulation of relativistic few-body s ystems with light-front field theories that maintain closer contact with Fe ynman diagrams. We find that Feynman diagrams distinguish Melosh rotations and other kinematical quantities belonging to various composite subsystem f rames that correspond to different loop integrals. The BT formalism knows o nly the rest frame of the whole composite system, where everything is evalu ated.