vertex style in tikz-feynman

Question

I'm getting used to the very nice TikZ-Feynman package! I'm trying to figure out how to add styles to a vertex, when using manual placement. For example I'd like the "blob" in the following to actually be a blob, not the word:

\documentclass[border=4mm]{standalone}
\usepackage{tikz} 
\usetikzlibrary{shapes,arrows,positioning,automata,backgrounds,calc,er,patterns}
\usepackage[compat=1.1.0]{tikz-feynman}

\begin{document}
\begin{tikzpicture}
\begin{feynman}
\vertex (pf) {$\underline{p}$};
\vertex [right=1cm of pf] (qf1) {$\underline{q}_1$};
\vertex [right=1cm of qf1] (qf2) {$\underline{q}_2$};
\vertex [right=1cm of qf2] (qf3) {$\underline{q}_3$};
\vertex [right=1cm of qf3] (qf4) {$\underline{q}_4$};

\vertex [below=5cm of pf] (pi) {$p$};
\vertex [right=1cm of pi] (qi1) ;
\vertex [right=1cm of qi1] (qi2) {$q_1$};
\vertex [right=1cm of qi2] (qi3) {$q_2$};
\vertex [right=1cm of qi3] (qi4);

\vertex [below=2.5cm of qf2] (c) {blob} ;

\diagram*{
 (pi) -- [scalar] (c) -- [scalar] (pf),
 {(qi2),(qi3)} -- (c),
 (c) -- {(qf1),(qf2),(qf3),(qf4)},
};


\draw [decoration = {brace} , decorate] (qf1.north west) -- (qf4.north east) node [pos = 0.5 , above = 0.125cm] {\underline{\alpha}};

\draw [decoration = {brace} , decorate] (qi3.south east) -- (qi2.south west) node [pos = 0.5 , below = 0.125cm] {\alpha};

\end{feynman}
\end{tikzpicture}

\end{document}

This produces:

I tried various things with the usual TikZ node syntax, but no luck. I like the default "blob" in TikZ-feynman but would be happy to just manually draw a big shaded-in circle in there. Thanks!

Answer 1

Looks like you can just add the usual keys to the options of the \vertex macro, e.g. \vertex [below=2.5cm of qf2,blob] (c) {blob};. The blob style is defined by tikz-feynman.

\documentclass[border=4mm]{standalone}    
\usepackage{tikz} 
\usetikzlibrary{shapes,arrows,positioning,automata,backgrounds,calc,er,patterns}
\usepackage[compat=1.1.0]{tikz-feynman}

\begin{document}
\begin{tikzpicture}
\begin{feynman}
\vertex (pf) {$\underline{p}$};
\vertex [right=1cm of pf] (qf1) {$\underline{q}_1$};
\vertex [right=1cm of qf1] (qf2) {$\underline{q}_2$};
\vertex [right=1cm of qf2] (qf3) {$\underline{q}_3$};
\vertex [right=1cm of qf3] (qf4) {$\underline{q}_4$};

\vertex [below=5cm of pf] (pi) {$p$};
\vertex [right=1cm of pi] (qi1) ;
\vertex [right=1cm of qi1] (qi2) {$q_1$};
\vertex [right=1cm of qi2] (qi3) {$q_2$};
\vertex [right=1cm of qi3] (qi4);

\vertex [below=2.5cm of qf2,blob] (c) {blob} ;

\diagram*{
 (pi) -- [scalar] (c) -- [scalar] (pf),
 {(qi2),(qi3)} -- (c),
 (c) -- {(qf1),(qf2),(qf3),(qf4)},
};


\draw [decoration = {brace} , decorate] (qf1.north west) -- (qf4.north east) node [pos = 0.5 , above = 0.125cm] {\underline{\alpha}};

\draw [decoration = {brace} , decorate] (qi3.south east) -- (qi2.south west) node [pos = 0.5 , below = 0.125cm] {\alpha};

\end{feynman}
\end{tikzpicture}

\end{document}