# Proper circle propagator loop using tikz-feynman package

Since I wasn't able to comment the answer to this question:

Propagator loop in Feynman diagram using tikz-feynman package

I need to ask separately. I was looking for the same thing except that I would like the propagator loop to be a proper circle. Does anybody know how this can be done?

%% luatex85 is only necesary to fix a bug in standalone
\RequirePackage{luatex85}
\documentclass{standalone}

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

\begin{document}
\feynmandiagram [horizontal=a to b, layered layout] {
a -- b [dot] -- [out=135, in=45, loop, min distance=3cm] b -- c,
};
\end{document}


It is possible to use the {feynman} environment within a {tikzpicture} which allows you to access all the commands from TikZ.

\RequirePackage{luatex85}
\documentclass{standalone}

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

\begin{document}
\begin{tikzpicture}
\begin{feynman}
\diagram [horizontal=a to b, layered layout] {
a -- b [dot]--b--c
};
\path (b)--++(90:0.5) coordinate (A);
\draw (A) circle(0.5);
\end{feynman}
\end{tikzpicture}
\end{document}


Output:

• That's quite nice! When using the feynman package this way, how can I manipulate the propagator circle characteristics, say I want it to be a [scalar]? – uitty400 Aug 23 '17 at 13:09
• @uitty400, which circle characteristics, radius? If it is, add \def\r{0.5} and change the code with \r. – ferahfeza Aug 23 '17 at 13:15
• no, as I said I want the circle to represent a scalar particle, which is usually done by the [scalar] option, so that the circle shows as a dotted line. – uitty400 Aug 23 '17 at 13:24
• @uitty400, \draw [dotted] (A) circle(\r); – ferahfeza Aug 23 '17 at 13:30