 Solution

ID: past-exam-of-the-particle-and-nuclear-physics-course-of-the-university-of-cambridge/2022/section-a/3/c/solution

There are five vertex types:

gggg, W^{+} W^{-} W^{+} W^{-}, W^{+} W^{-} ZZ, W^{+} W^{-} Z γ, W^{+} W^{-} γγ .

The quartic terms arise from the square of the quadratic-field piece of the non-Abelian gauge field strength. Every electroweak quartic gauge boson self-interaction contains a

W^{+} W^{-}

pair. The absence of a fundamental purely neutral quartic vertex does not forbid amplitudes such as light-by-light scattering: those can be generated by loop diagrams, rather than by a single fundamental interaction vertex.

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