A. Zee, Quantum Field Theory in a Nutshell · Problem II.8.1

Field Theory Redux

Physics — QFT

Problem

Show that averaging and summing over photon polarizations amounts to replacing the square bracket in (9) by

2[\frac{\omega'}{\omega} + \frac{\omega}{\omega'} - \sin^2 \theta]

. [Hint: We are working in the transverse gauge.]