I am studying QFT from Srednicki's book. Let me ask a question about symmetry factor from this book.(adsbygoogle = window.adsbygoogle || []).push({});

Let, for specific values of [itex]V[/itex] and [itex]P[/itex] from eqn (9.11) we get some terms. One of them is a disconnected diagram consisted of two connected diagrams [itex]C_1[/itex] and [itex]C_2[/itex]. The disconnected diagrams symmetry factor is, say, S; that is the term for disconnected diagram has a numerical coefficient: [itex]\frac{1}{S}[/itex]. Now we write the term for disconnected diagram according to the eqn (9.12): [itex] D = \frac{1}{S_D} \prod_I (C_I)^{n_I} [/itex]. In this case is this true: [itex]S=\frac{1}{n_1 !} \times \frac{1}{n_2!} \times C_1 [/itex]'s symmetry factor [itex]\times C_2[/itex]'s symmetry factor? Here, [tex]S_D = \prod_I n_I ![/tex]

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# Symmetry factor of a general feynman diagram

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