I'm working through Srednicki's QFT text, and I'm continuously vexed by the various numerical factors in diagrams and vertices, as well as the grouping of diagrams. For example, in Chapter 10 (pg 75) Srednicki treats basic [tex]\phi\phi\rightarrow\phi\phi[/tex] scattering processes in [tex]\phi^3[/tex]. He claims the 4 sources on the interaction yield 4!=24 different diagrams (alright), collected in 3 different groups (hmm) with 8 graphs each (which "neatly cancels the symmetry factor"?).(adsbygoogle = window.adsbygoogle || []).push({});

Each of those statements seems logical, and the first two make some sense (I know the basic digram, and have read elsewhere you can "twist" diagrams to get the 3 groups he comes up with). Mathematically or intuitively, though, how can I look at this problem and see that there are indeed 3 kinds of diagram AND know that they each have 8-fold degeneracy?

It's this final bit that I cannot quite grasp; any help would be appreciated.

Thanks!

Tom

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# Counting and Grouping Feynman Diagrams

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