Feynman diagram

Summary

A Feynman diagram is a graph that labels one term in the perturbation series of a quantum field theory. Its edges carry propagators, and its internal vertices carry the coupling constants of the interaction. Its value is an integral over the positions or momenta of the internal vertices. By Wick's theorem, each order of perturbation theory is a finite sum over diagrams. Diagrams organize the computation of scattering amplitudes and make divergences and renormalization visible graph by graph.