SU2 gauge self-interaction vertices
= SU2 gauge self-interaction vertices
{c}
For field strength $F^a_{\mu\nu}=f^a_{\mu\nu}-g\epsilon^{abc}A_\mu^bA_\nu^c$, the square produces $\mathcal L_3=g\epsilon^{abc}(\partial_\mu A_\nu^a)A^{b\mu}A^{c\nu}$ and $\mathcal L_4=-g^2\epsilon^{abc}\epsilon^{ade}A_\mu^bA_\nu^cA^{d\mu}A^{e\nu}/4$. The cubic <Feynman vertex> has one derivative; the quartic one has none. No higher pure-gauge vertex occurs.