Consider the following code written using the tikz-feynman
package:
\RequirePackage{luatex85}
\documentclass{standalone}
\usepackage[compat=1.0.0]{tikz-feynman}
\begin{document}
\feynmandiagram [horizontal=a to b] {
a -- b [dot] -- [out=135, in=45, loop, min distance=3cm] b -- c,
};
\end{document}
This draws the following Feynman diagram:
I would like to make the line completely horizontal and turn the loop from an oval into a sphere?
How do you do this?
Best Answer
The issue here is that the algorithm that TikZ-Feynman (CTAN) uses in order to place the vertices doesn't work well if it only has a straight line because the difference in the optimization between a mostly-straight and a fully-straight line are quite small.
This can be easily fixed by using an alternative layout algorithm, such as the layered layout in this case: