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Finally, I solved it by:

\begin{tikzpicture}
\begin{feynman}[large]
\vertex (b);
\vertex [left=of b, crossed dot,draw=black,fill=white] (a) {};
\vertex [above right=of a] (i1);
\vertex [below right=of a] (i2);
\vertex [right=3 cm of a](d);
\vertex [right=of d, crossed dot,draw=black,fill=white] (c ...

Hi,

I was looking for a diagram such as shown in the first picture, but I just get the one that is in the second picture with this code:

\begin{tikzpicture}
\begin{feynman}[large]
\vertex (b);
\vertex [left=of b] (a);
\vertex [above right=of a] (i1);
\vertex [below right=of a] (i2);
\vertex (d ...