# Feynman Diagram (with Tikz-Feynman) that involves a big blob

I'm new to Latex and wanted to use a certain Feynman Diagram. My problem is, that I don't know, how to draw something like this with Tikz-Feynman:

It's supposed to be a 4-point vertex, where the interaction is represented by the oval blob and transmits momentum P. The arrows at the end of the legs represent the spin. It would be nice, if someone had a suggestion for making such a thing, with a special label for the text (where I could fill in the momenta/ spin)

• Sry, for double-posting, but I couldn't find a button for editing. My second question is: how do I create Feynman-Diagrams with tikz-feynman, so that the resulting diagrams can be added as figures (and seen in the list of figures)? – Zyrax Aug 14 '16 at 22:01

You have to position the vertices manually.

\documentclass{article}
\usepackage{tikz-feynman,contour}
\begin{document}
\begin{figure}
\centering
\begin{tikzpicture}
\begin{feynman}
\vertex[blob,label={right:$p$}] (m) at ( 0, 0) {\contour{white}{$\uparrow$}};
\vertex (a) at (-1,-2) {$\uparrow$};
\vertex (b) at ( 1,-2) {$\downarrow$};
\vertex (c) at (-1, 2) {$\uparrow$};
\vertex (d) at ( 1, 2) {$\downarrow$};
\diagram* {
(a) -- [fermion,edge label=$-k$] (m) -- [fermion,edge label=$-k'$] (c),
(b) -- [fermion,edge label'=$k+p$] (m) -- [fermion,edge label'=$k'+p$] (d),
};
\end{feynman}
\end{tikzpicture}
\caption{Scattering at a 4-vertex.}
\end{figure}
\end{document}


• Thanks a lot, that is perfect! And do you maybe know, how I can treat those feynman diagrams like "ordinary" figures? So that they are automatically added to the list of figures? – Zyrax Aug 15 '16 at 15:19
• Perfect, that worked too, thanks a lot! Last question: How can I center the diagrams? Every diagram of mine is on the left, but I want the figure in the middle. I tried begin/end{center}, but it didn't work. – Zyrax Aug 17 '16 at 16:52
• I did that, but it will not be "recorded", because my current reputation is not enough. – Zyrax Aug 30 '16 at 13:47
• Maybe I should ask this as a separate question but the question seems so small? How do I replace the blob with an unfilled circle, so no shading. This should be so simple but I can't find how. – Kvothe Nov 20 '17 at 10:00
• @Kvothe \vertex[draw,circle] {$\uparrow$};? – Henri Menke Nov 20 '17 at 19:53