tikz-feynman package - making a diagram symmetrical

Question

I have the following code which draws a Feynman diagram using the tikz-feynman package.

\feynmandiagram [baseline={(current bounding box.center)},medium, vertical=b to f] {
        a [nudge=(-30:5mm)]
        -- [photon, edge label=\(p_{1}\)] b [label=190:\(\mu_{1}\)]
        -- [fermion, edge label=\(k_{2}\)] c,
        d[nudge=(210:5mm)] -- [photon, edge label'=\(p_{2}\)] c [label=-30:\(\mu_{2}\)],
        c -- [fermion, edge label=\(k_{3}\)] e [label=0:\(\mu_{3}\)] -- [fermion, edge label=\(k_{4}\)] f [label=180:\(\mu_{4}\)] -- [ fermion, edge label=\(k_{1}\)] b,
        g [nudge=(-30:5mm)] -- [photon, edge label'=\(p_{3}\)] e,
        h [nudge=(-30:5mm)] -- [photon, edge label'=\(p_{4}\)] f,
    };

Here is the diagram which can be drawn using the code.

How do I make the bottom two wavy external lines the same length as the top two wavy external lines?

I would like to make the diagram symmetrical.

Answer 1

You are nudging all the vertices, but all in the same direction. That is, you are pushing all of the outer vertices by 5mm at an angle of -30° (that is, to the right and slightly down). If you remove the nudging, the diagram looks symmetric:

\documentclass[tikz]{standalone}

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

\begin{document}
\feynmandiagram [baseline={(current bounding box.center)},medium, vertical=b to f] {
  a
    -- [photon, edge label=\(p_{1}\)] b [label=180:\(\mu_{1}\)]
    -- [fermion, edge label=\(k_{2}\)] c,
  d -- [photon, edge label'=\(p_{2}\)] c [label=0:\(\mu_{2}\)],
  c -- [fermion, edge label=\(k_{3}\)] e [label=0:\(\mu_{3}\)]
    -- [fermion, edge label=\(k_{4}\)] f [label=180:\(\mu_{4}\)]
    -- [fermion, edge label=\(k_{1}\)] b,
  g -- [photon, edge label'=\(p_{3}\)] e,
  h -- [photon, edge label'=\(p_{4}\)] f,
};
\end{document}

If you want to keep the nudging (not sure why?), then make sure to adjust the direction of the nudging accordingly:

\documentclass[tikz,border=10pt]{standalone}

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

\begin{document}
\feynmandiagram [baseline={(current bounding box.center)},medium, vertical=b to f] {
  a [nudge=(135:1cm)]
    -- [photon, edge label=\(p_{1}\)] b [label=180:\(\mu_{1}\)]
    -- [fermion, edge label=\(k_{2}\)] c,
  d [nudge=(45:1cm)]
    -- [photon, edge label'=\(p_{2}\)] c [label=0:\(\mu_{2}\)],
  c -- [fermion, edge label=\(k_{3}\)] e [label=0:\(\mu_{3}\)]
    -- [fermion, edge label=\(k_{4}\)] f [label=180:\(\mu_{4}\)]
    -- [fermion, edge label=\(k_{1}\)] b,
  g [nudge=(-45:1cm)]
    -- [photon, edge label'=\(p_{3}\)] e,
  h [nudge=(-135:1cm)]
    -- [photon, edge label'=\(p_{4}\)] f,
};
\end{document}