I modified a sample from this source :
http://osksn2.hep.sci.osaka-u.ac.jp/~taku/osx/fmfsamples.pdf
(Look for 5.3 Cross diagram) and my aim is to label every of the "four" fermion propagators with an impuls.
My problem is that displaying a crossed diagram only gives me to propagators to label, but I want to have four. So my questions are : 1. Is there a nice way to label 2 propagators with 4 impulses? 2. Is there a better way to code a four propagator crossed diagram (to display a four-quark operator)?
\begin{fmffile}{Diagram0th}
\begin{fmfgraph*}(100,100)
\fmfleft{i1,i2}
\fmfright{o1,o2}
\fmflabel{$x_3$}{i1}
\fmflabel{$x_1$}{i2}
\fmflabel{$x_4$}{o1}
\fmflabel{$x_2$}{o2}
\fmflabel{z}{v1}
\fmf{fermion, label=$p_1$}{i1,v1,o2}
\fmf{fermion}{i2,v2,o1}
\fmf{photon}{v1,v2}
\fmfv{decoration.shape=square}{v1}
\end{fmfgraph*}
\end{fmffile}
Best regards, Dirk