Blob not appearing at vertex

[Isanderson]

I am trying to generate a mu \to e \gamma diagram with an effective operator at the vertex. My current code for the diagram is

\begin{feynman}
  \vertex (a1) {\(\mu\)};
  \vertex[right=1.5cm of a1, blob] (a2);
  \vertex[right=1.5cm of a2] (a3) {\(e\)};
  \vertex[above=1cm of a3] (p){\(\gamma \)};

  \diagram* {
    (a1) -- [fermion, momentum' = \( p \)] (a2) -- [fermion, momentum' = \(p-q\)] (a3),
    (a2) -- [photon, momentum = \(q\)] (p)
  };
\end{feynman}

However it does not generate the blob (it generates the rest of the diagram just fine).

I cannot figure out why not - any ideas?

[JP-Ellis]

This seems to be a bug in the way styles are handled when created through the \vertex command which will need to be fixed.

In the mean time, you can use:

\begin{feynman}
  \vertex (a1) {\(\mu\)};
  \node[right=1.5cm of a1, blob] (a2) {};
  \vertex[right=1.5cm of a2] (a3) {\(e\)};
  \vertex[above=1cm of a3] (p){\(\gamma \)};

  \diagram* {
    (a1) -- [fermion, momentum' = \( p \)] (a2) -- [fermion, momentum' = \(p-q\)] (a3),
    (a2) -- [photon, momentum = \(q\)] (p)
  };
\end{feynman}

which should produce what you want.

[Isanderson]

The temporary solution works just fine, thanks!

[losmaxos]

Hi, I think this is due to the way TikZ handles node drawing. Nodes are only drawn if they have a name argument. If you include an empty nsame argument after the blob vertex, it will be drawn just fine:

\vertex[right=1.5cm of a1, blob] (a2) {};

Hope this helps, greetings to the maintainer of Tikz-Feynman!