Furry theorem

If all photons are real, such a diagram is forbidden.

The Furry theorem , named after the US physicist Wendell Furry , is a theorem of quantum electrodynamics . It says that Feynman diagrams , the only outer lines of which are photons , vanish if the number of outer photons is odd . In particular, due to the Furry theorem, no single photon can arise or be destroyed from the vacuum . So it is an immanent component of energy conservation .

The Furry theorem is based on the invariance of the vacuum under charge conjugation (C-invariance) and the symmetry of the photon-fermion vertex under such. It is therefore not valid for non-Abelian gauge theories in which C-odd contributions also occur. In particular, a scattering of three real gluons is not forbidden, but proportional to the structure constant of the associated Lie algebra .

Individual evidence

1. ^ NV Smolyakov: Furry theorem for non-abelian gauge Lagrangians . In: Teoreticheskaya i Matematicheskaya Fizika . tape 50 , no. 3 , 1981, p. 344-349 .

literature

• Michael D. Peskin and Daniel V. Schroeder: An Introduction to Quantum Field Theory . Perseus Books Publishing, 1995, ISBN 0-201-50397-2 .