feynlag.export.ufo.vvvv.adjoint_vvvv¶

feynlag.export.ufo.vvvv.adjoint_vvvv(group, feynman_rule=True)[source]¶

Colour-stripped VVVV coupling of an UNBROKEN non-abelian group.

An unbroken group’s 4-boson vertex is ONE UFO particle repeated four times, with the adjoint index carried by the colour tensors ADJOINT_VVVV_COLORS. The coupling that pairs with them must therefore be colour-stripped.

quartic_couplings works in the weak basis, where its entry for a component quadruple is -g^2/4 * sum_e f_{ije} f_{kle} — it already contains the colour contraction. Feeding those component-specific values to the writer alongside a colour tensor multiplies by colour twice, which is what tests/test_ufo_qcd.py did before this helper existed. Divide it out and the result is i g^2 on every structure, independent of N — matching MadGraph’s stock sm GC_12 = i*G**2 for [g,g,g,g] (pinned in tests/test_yangmills.py::TestMadGraphOracle).

Returns:: {VVVV1/2/3: coupling}, to be emitted with ADJOINT_VVVV_COLORS.