File:OZI rule - Feynmann diagram2.svg

\documentclass[tikz]{standalone}
\usepackage{tikz-feynman}

\begin{document}
	\footnotesize
\begin{tikzpicture}[dot/.style={draw,shape=circle,fill=black},scale=1.2]
	\begin{feynman}
		\vertex at (-.2,0) 				(d1) {$d$};
		\vertex at (.2,0) 				(d2) {$d$};
		\vertex at ($(d1)-(2,0)$) 		(d3) {$d$};
		\vertex at ($(d2)+(2,0)$) 		(d4) {$d$};
		\vertex at ($(d3)-(.4,0)$) 		(u1) {$u$};
		\vertex at ($(d4)+(.4,0)$) 		(u2) {$u$};
		\vertex at ($(d1)+(-.7,-2)$) 	(g11);
		\vertex at ($(d2)+(.7,-2)$) 	(g12);
		\vertex at (0,-4) 				(g1);
		\vertex at ($(g11)-(0,3.2)$) 	(g21);
		\vertex at ($(g12)-(0,3.2)$) 	(g22);
		\vertex at ($(g1)-(0,1)$) 		(g2);
		\vertex at ($(d1)-(0,6.5)$) 	(s1) {$s$};
		\vertex at ($(d2)-(0,6.5)$) 	(s2) {$s$};

		\diagram {
			(d3) -- [fermion] (g11) -- [fermion] (d1),
			(d2) -- [fermion] (g12) -- [fermion] (d4),
			(u2) -- [fermion] (g1)  -- [fermion] (u1),
			(g11) -- [gluon,pos=.75,edge label=$g$] (g21),
			(g12) -- [gluon,pos=.75,edge label=$g$] (g22),
			(g1) -- [gluon,pos=.41,edge label=$g$] (g2),
			(s1) -- [fermion] (g21) -- [fermion] (g2) -- [fermion] (g22) -- [fermion] (s2),
		};

		\draw [dashdotted,thick] (u1) ++(0,-4.8) -- ++(5,0) node [above=-9pt, pos=.95,text width=1cm] {\tiny imaginary cut axis};

		\draw [decoration={brace}, decorate] (d4.north west) -- node[above] {$\pi^-$} (u2.north east);
		\draw [decoration={brace}, decorate] (u1.north west) -- node[above] {$\pi^+$} (d3.north east);
		\draw [decoration={brace}, decorate] (d1.north west) -- node[above] {$\pi^0$} (d2.north east);
		\draw [decoration={brace,mirror}, decorate] (s1.south west) -- node [below] {$\phi$} (s2.south east);

		\node [dot,scale=.5] at (g11) {};
		\node [dot,scale=.5] at (g12) {};
		\node [dot,scale=.5] at (g21) {};
		\node [dot,scale=.5] at (g22) {};
		\node [dot,scale=.5] at (g1) {};
		\node [dot,scale=.5] at (g2) {};

	\end{feynman}
\end{tikzpicture}
\end{document}