In tikz-feynman, I want to draw a curved arc between two points, and then attach a loop to this. Here is an extremely hack version I did as a stopgap:
\documentclass{article}
\usepackage{tikz}
\usepackage[compat=1.1.0]{tikz-feynman}
\begin{document}
\begin{tikzpicture}
\begin{feynman}
\vertex (t) at (0,2);
\vertex (b) at (0,-2);
\vertex (lt) at (-0.5,1);
\vertex (lm) at (-1,0);
\vertex (lb) at (-0.5,-1);
\vertex (rt) at (0.5,1);
\vertex (rm) at (1,0);
\vertex (rb) at (0.5,-1);
\diagram*{
(t) -- (lt) -- (lm) -- (lb) -- (b),
(t) -- (rt) -- (rm) -- (rb) -- (b),
(lt) -- [gluon] (lb),
};
\end{feynman}
\end{tikzpicture}
\end{document}
which produces
I hope the idea is clear enough. This would be adequate for my purposes except that I want the lines to be curved, i.e. this should be two arcs between (t) and (b), not this ugly diamond-shaped thing. I think what I want to do is just draw the two arcs from (t) to (b) and then define some vertices "along the arcs" with which I can make the gluon line, but have struggled to figure out how to do this.
Because this diagram is part of a larger equation of diagrams, I would prefer to use absolute vertex positions for at least (t) and (b).