HELP: Photon: Completeness relation

elmerx25

Hello:

does anybody knows how can I demostrate this relation:?



[tex] \sum_{\lambda = R, L} (\epsilon_{\lambda})^*_i (\epsilon_{\lambda})_{j} = \delta_{i, j} - \hat q_{i} \hat q_{j} [/tex]



Thanks.

P.S.: Exercise 6.12 of "Quarks and Leptons. An Introductory Course in Modern Particle Physics - F.Halzem,A.Martin"