...like in Photon-Photon-scattering. I know this doesn't make sense physically but the value for the diagram should still be computeable. If I want to put the expression for the matrix element together, I get a matrix, but it should be a scalar, right? Since the spinor bi-product is missing....(adsbygoogle = window.adsbygoogle || []).push({});

Do I have to take the trace?

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# Evaluating Feynman diagram in QFT without external fermion lines

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