# Issues with feynman diagram vertex

I'm unable to put more then one label on a vertex in a Feynman diagram. I've tried to use the command \fmfv twice or with more then one argument, but sadly I'm not getting the result I wished for. Does anyone have a suggestion to offer me?

\documentclass[a4paper, 10pt]{report}
\usepackage{feynmp-auto}
\begin{document}
\begin{fmfgraph*}(200,100)
\fmfleft{i}
\fmfright{o}
\fmf{boson}{i,v1}
\fmf{fermion,left}{v1,o,v1}
\fmflabel{\alpha}{i}
\fmfv{label=$z_{1}$,label.angle=180}{i}
\fmfv{label=$z_{1}^{'}$,label.angle=0}{v1}
\fmfdot{i}
\fmfdot{v1}
\end{fmfgraph*}
\end{fmffile}\\
\end{document}

• Welcome! Please provide us with a minimal working example (MWE) i.e. a complete but small document demonstrating the issue. Please also specify what result you wished for and how that differs from the result we get when we compile your code. – cfr May 25 '16 at 15:49
• Thanks mate!\begin{fmffile}{tadpole_diagram} \begin{fmfgraph*}(200,100) \fmfleft{i} \fmfright{o} \fmf{boson}{i,v1} \fmf{fermion,left}{v1,o,v1} \fmflabel{\alpha}{i} \fmfv{label=$z_{1}$,label.angle=-90}{i} \fmfv{label=$z_{1}^{'}$,label.angle=0}{v1} \fmfdot{i} \fmfdot{v1} \end{fmfgraph*} \end{fmffile}\\ – Richard May 25 '16 at 18:02
• That is the code, however i cannot put more labels in each vertex, for example in the z_1 vertex i wish to put a label Lambda and Mu for the spin indices – Richard May 25 '16 at 18:04
• Please edit your question to add the code and make it into a complete minimal document we can compile i.e. start \documentclass{} ... and include any required packages. (Not your whole preamble - just what's needed for the example. Others may know, but I have no idea how to make your code compilable. – cfr May 25 '16 at 18:10

Since FeynMp doesn't seem to allow this, I can offer an alternative using a different package: TikZ-Feynman (CTAN).

It is built on top of TikZ and allows for several labels on vertices. Here's an example that places multiple labels:

\documentclass[tikz, convert]{standalone}

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

\begin{document}
\feynmandiagram [layered layout, horizontal=a to b] {
a [particle={$$z_{1}, \alpha$$}]
-- [boson] b [label=0:$$z_{1}'$$, label=120:$$\mu$$]
-- [half left, fermion] c [label=60:Foo, label=-60:Bar]
-- [half left, fermion] b,
};
\end{document}


I don't really know what labels you want, so these are just dummy labels, but hopefully that gives you a starting point.

• I've tried your package, but it seems to not draw properly some diagrams, like the s-channel. And a question mark appears from nowhere too!! How do i fix this? – Richard May 27 '16 at 17:32
• @Richard To draw an s-channel, have a look through the documentation and if that doesn't help, you're quite welcome to post here or on the Github page. I also have never had question marks appear, so if you think it is a bug, go ahead and open an issue on Github. – JP-Ellis May 28 '16 at 2:37
• No worries everything has been solved. Thanks mate. I just have another question; it is possible to put a dot in a vertex as in feymnp? – Richard May 28 '16 at 10:41
• Yes it is, with the dot style (which is in the documentation ;) ) – JP-Ellis May 28 '16 at 11:07
• Thanks mate i've just seen it but if the dot come to big never mind. By the way everything works fine. if anyone needs this two diagrams remember to thank JP Ellis for his brilliant package. – Richard May 29 '16 at 20:45

This is not possible. From the package manual, p. 23:

In the current implementation, there can be only a single label for each vertex. Thus earlier calls to \fmflabel for the same vertex will be overwritten.