Operator matrix element Feynman diagrams

Question

I am trying to draw the following cutted diagram

but I don't know how to do it.

I am using feynmf for the Feynman diagrams for my thesis since tikz-feynman requires lualatex and it gives enormous compiling times.

On a more general note, I would like to know these Wick contraction diagrams are usually made

As far as I know, there isn't any specific package to do them beside tikz which is a bit cumbersome and I really would like to avoid it!

Answer 1

I haven't used feynmf/feynmp in ages, so this is unfortunately all I can offer:

\documentclass{article}

\usepackage{feynmp-auto}

\begin{document}

\begin{fmffile}{diagram}
\begin{fmfgraph*}(100,50)
\fmfstraight
\fmfleft{k,o} \fmflabel{$K^+$}{k}
% po=neutral pion; pm= help point for phantom line; pz=useless;pp=charged pion
\fmfright{po,pm,pz,pp}\fmflabel{$\pi^0$}{po}\fmflabel{$\pi^+$}{pp}
\fmftop{t}% help vertex
\fmf{plain,right=.2}{k,po}
\fmf{plain,left=.2}{k,v2,po}
\fmf{phantom}{t,v2}
\fmffreeze
\fmf{plain,right=.6,tension=.5}{pp,v1,pp}
\fmf{dashes,left=.3}{v2,v1}
\fmf{phantom,tension=.6}{o,vl}\fmf{plain,tension=2,left=.1,fore=red}{vl,vr}\fmf{phantom}{vr,pm}
\end{fmfgraph*}
\end{fmffile}

\end{document}