6

I would like to produce the following Feynman diagram using the TikZ-Feynman package.

image

So far this is what I have:

\begin{tikzpicture}
\begin{feynman}
\vertex (li);
\vertex [below=2cm of li] (hi);
\vertex [right=of li] (a);
\vertex [above right=of a] (lf);
\vertex [below right=of a] (b);
\vertex [right=of b] (hf1);
\vertex [blob, right=of hi] (c) {};
\vertex [below right=of c] (hf2);

\diagram* {
    (li) -- [fermion] (a) -- [fermion] (lf),
    (hi) -- [fermion] (c) -- [fermion] (hf2),
    (a) -- [photon] (b) -- [fermion] (hf1),
    (c) -- [fermion] (b),
};
\end{feynman}
\end{tikzpicture}

which produces the following

enter image description here

What I'm having issues with is drawing three parallel lines that go into a single blob. If I generate three vertically-stacked vertices to the left of the blob and draw lines between them and the blob, clearly the lines are not gonna be parallel. If I "cheat" and draw three vertices within the blob itself, so that the three lines are parallel, the lines are drawn on top of the underlying blob. Clearly then neither of these methods works. Any help would be much appreciated.

1
  • 1
    As for your just deleted question: it looks to me a bit like a \textpsi. \documentclass{article} \usepackage{textgreek} \newcommand{\varpsi}{\mathord{\mbox{\textpsi}}} \begin{document} \textpsi$\psi\varpsi$ \end{document}
    – user194703
    May 16, 2020 at 8:13

1 Answer 1

5

Something like this?

\documentclass[tikz,border=3mm]{standalone}
\usepackage{tikz-feynman}
\begin{document}
\begin{tikzpicture}
\begin{feynman}
\vertex (li);
\vertex [below=2cm of li] (hi);
\vertex [right=of li] (a);
\path (a) ++ (20:2) node[vertex] (lf);
\vertex [below right=of a] (b);
\vertex [right=of b] (hf1);
\vertex [blob, right=of hi] (c) {};
\path (c.-10) ++ (00:2) node[vertex] (hf2);
\path (c.-40-|hf2.center) node[vertex] (hf3);

\diagram* {
    (li) -- [fermion] (a) -- [fermion] (lf),
    (hi) -- [fermion] (c) -- [fermion] (b),
    (a) -- [photon] (b) -- [fermion] (hf1),
    (c.-10) -- [fermion] (hf2),
    (c.-40) -- [fermion] (hf3)
};
\end{feynman}
\end{tikzpicture}
\end{document}

enter image description here

You may want to nudge the positions of the arrows a bit.

\documentclass[tikz,border=3mm]{standalone}
\usepackage{tikz-feynman}
\begin{document}
\begin{tikzpicture}
\begin{feynman}
\vertex (li);
\vertex [below=2cm of li] (hi);
\vertex [right=of li] (a);
\path (a) ++ (20:2) node[vertex] (lf);
\vertex [below right=of a] (b);
\vertex [right=of b] (hf1);
\vertex [blob, right=of hi] (c) {};
\path (c.-5) ++ (00:2) node[vertex] (hf2);
\path (c.-40-|hf2.center) node[vertex] (hf3);

\diagram* {
    (li) -- [fermion] (a) -- [fermion] (lf),
    (hi) -- [fermion] (c) -- [fermion] (b),
    (a) -- [photon] (b) -- [fermion] (hf1),
    (c.-5) -- [fermion] (hf2),
    (c.-40) -- [with arrow=0.52] (hf3)
};
\end{feynman}
\end{tikzpicture}
\end{document}

enter image description here

Source of inspirations: tikzfeynman.keys.code.tex.

5
  • That's lovely, thanks! Mar 29, 2020 at 14:29
  • Surely upvoted! Just two suggestions (if they are possible); but is it possible to have the line more tick and the tip of the arrow similar to the initial picture? Thank you very much.
    – Sebastiano
    Mar 29, 2020 at 16:42
  • 2
    @Sebastiano I actually like the arrows of feynmp most and am sometimes debating if I should write a short add-on that allows one to add similar arrows to tikz-feynman, along with arrows that indicate the fermion flow. Since you are living in Sicily you undoubtedly know why the latter is important. ;-)
    – user194703
    Mar 29, 2020 at 17:40
  • @Schrödinger'scat Maybe I have understood... to stop the flow.... pandemic? :-) These days... I don't understand anything. I hope very much that we return to normal and find a solution. I wish you all the best.
    – Sebastiano
    Mar 29, 2020 at 17:50
  • 2
    @Sebastiano No, it has to do with Majorana fermions.
    – user194703
    Mar 29, 2020 at 19:21

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