Feynman versus Bakamjian-Thomas in Light Front Dynamics

TL;DR

This paper compares two approaches to relativistic few-body systems, highlighting how Feynman diagrams reveal kinematical differences that the Bakamjian-Thomas formalism overlooks, especially in composite subsystem frames.

Contribution

It provides a detailed comparison showing the limitations of the Bakamjian-Thomas approach relative to light front field theories that incorporate Feynman diagram insights.

Findings

Feynman diagrams distinguish Melosh rotations and kinematical quantities.

Bakamjian-Thomas formalism evaluates only the rest frame of the entire system.

Differences are linked to loop integrals and subsystem frame evaluations.

Abstract

We compare the Bakamjian-Thomas (BT) formulation of relativistic few-body systems with light front field theories that maintain closer contact with Feynman diagrams. We find that Feynman diagrams distinguish Melosh rotations and other kinematical quantities belonging to various composite subsystem frames that correspond to different loop integrals. The BT formalism knows only the rest frame of the whole composite system, where everything is evaluated.