Vector boson scattering vertex

[gpinnaan]

When I draw a diagram with a 4 line vertex the line are always horizontal or vertical.

\feynmandiagram [] {
  i1 -- [boson ,  edge label=\(W^+\)] a -- [photon,  edge label=\(W^-\)] i2,
  f1 -- [photon,  edge label=\(Z\)]  a -- [photon,  edge label=\(Z\)] f2,
};

Is there any simple way to have diagonal lines instead?

[JP-Ellis]

You can use the vertical=⟨node⟩ to ⟨node⟩ (and similarly horizontal and the primed counterparts) key to change the orientation of the diagram. As I mention in the documentation, the two vertices need not be neighbours, so you can have horizontal=i1 to i2.

There are other issues with your example though. You have edge label=(W^+), but I'm not sure you really want this to be parenthesised. Did you intend to have a math environment, because this requires \(…\)—note the backslash \ before the opening and closing parenthesis. I'm also not sure why you have the empty [] after \feynmandiagram. In LaTeX, [] is conventionally used to indicate optional arguments, and if no optional arguments are required, they can be omitted.

Is this what you want:

\RequirePackage{luatex85}
\documentclass[border=10pt]{standalone}

\usepackage[compat=1.1.0]{tikz-feynman}

\begin{document}
\feynmandiagram [vertical'=i1 to i2] {
  i1 [particle=\(W^{+}\)] -- [boson] a -- [boson] i2 [particle=\(W^{-}\)],
  f1 [particle=\(Z\)] -- [boson] a -- [boson] f2 [particle=\(Z\)],
};
\end{document}