A General Expression for Symmetry Factors of Feynman Diagrams
The calculation of the symmetry factor corresponding to a given Feynman diagram is well known to be a tedious problem. We have derived a simple formula for these symmetry factors. Our formula works for any diagram in scalar theory ($ϕ^3$ and $ϕ^4$ interactions), spinor QED, scalar QED, or QCD.
hep-th↗