Proof of Furry's theorem

i was wondering if anyone could give an explicit calculation or show a link that shows the proof to Furry's theorem. showing how the vacuum expectation value of any odd number of electromagnetic currents vanishes. in particular the case for $n=3$.

• Wait, are you after the n=3 or the n=1 case? – Michael Oct 1 '13 at 13:54
• i was after the photon one loop n=3 case. – alejandro123 Oct 1 '13 at 14:24
• Did you just try to copy the question from here, almost word for word?? physics.stackexchange.com/q/54812 – nervxxx Oct 1 '13 at 21:31
• @alejandro123 : See a short proof here in .pdf format. It is the first result in google. – Flint72 May 23 '14 at 19:46
• I was looking for an actual proof carrying out the calculation of the integral from Feynman's diagram. – alejandro123 May 26 '14 at 10:51

This comes from the fact that the electromagnetic current changes sign under charge conjugation i.e $Cj^{\mu\nu}C^{\dagger} = -j^{\mu\nu}$ and thus the vaccum expectation of all diagrams withodd number of em legs vanishes