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kexue
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In Srednicki's QFT book on page 63, figure 9.11, the diagram in the middle of the second row is a Feynman diagram with four external lines, two vertices, one internal line and one loop placed on one external line. It has symmetry factor 4.
Does the symmetry facor stand for the 4 possibilities to place the loop on all four external lines respectively, so that these four diagrams would be equivalent?
thanks
Does the symmetry facor stand for the 4 possibilities to place the loop on all four external lines respectively, so that these four diagrams would be equivalent?
thanks