When computing the propagator of the $Z$ boson at one-loop level in the Standard Model, should we consider both of these two diagrams (where $\varphi^\pm$ are the charged Goldstone bosons) or are they the same diagram and should only be considered once?
1 Answer
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Think about how Feynman diagrams originate from the perturbative expansion. These two diagrams will come from different terms in the expansion, so they are not the same.