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I am trying to create some feynman diagrams with tikz. My problem is, that I want to create some simple diagrams like vacuum diagrams in φ^4 theory, which are reducible though, so I don't know where to put the vertices and the nodes. For the simplest two point function of free scalar field diagram for example I use this code:

\feynmandiagram [horizontal=a to b,horizontal=c to d] {
a[particle=$x_1$] -- b[particle=$x_2$],
c[particle=$x_3$] -- d[particle=$x_4$],
};+\feynmandiagram [vertical=a to b,vertical=c to d] {
a[particle=$x_1$] -- b[particle=$x_2$],
c[particle=$x_3$] -- d[particle=$x_4$],
};

which just gives

this image

which apparently isn't what i want,the desired diagram is :

enter image description here

I think the problem lies on the horizontal command which I don't know if stands for more than one variable, I just don't know how to fix it.

  • Welcome to TeX.SX! The second image is missing. – dexteritas Aug 8 '17 at 15:16
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    Having not seen the second image: Try compiling with lualatex instead of pdflatex/xelatex. The tikz-feynman package makes use of Lua for positioning stuff, so you won't always get the best results with pdflatex – Torbjørn T. Aug 8 '17 at 15:48
  • Please extend your code to a minimal working example (MWE). – dexteritas Aug 8 '17 at 15:56
  • I editted so you can see the second picture. I have tried lualatex which merely saves the day, since the visuals get better but i still cant get two parallel lines vertically and two parallel lines horizontally as i wish. Meanwhile when i compile whiti lualatex ,my whole text dissaperas, i guess because its in greek which doesnt help – Ian Morison Aug 8 '17 at 19:06
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TikZ-Feynman (CTAN) can only use on horizontal directive, and in addition doesn't really know how to handle disconnected diagrams.

The solution in your case is actually pretty simple: just connect the diagrams so that the algorithm can handle everything nicely, but then use draw=none so that the lines aren't actually drawn.

Here's an example for your first one:

\RequirePackage{luatex85}
\documentclass[tikz, border=1em]{standalone}

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

\begin{document}
\feynmandiagram [horizontal=a to b] {
  a [particle=$x_1$] -- b [particle=$x_2$],
  c [particle=$x_3$] -- d [particle=$x_4$],
  {[edges={draw=none}]
    a -- c, b -- d,
  },
};
\end{document}

output

If you want to fine tune the placement of the lines and their separation, it might be easier to then specify the placement of vertices as shown in the TikZ-Feynman manual.

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