Tikz-feynman [blob] does not appear

Question

I am trying to create a simple fermion that has both a blob and horizontally aligned paths. However, I cannot get my diagram to work with both.

1. With \feynmandiagram, I can create a blob, but not a horizontal outgoing fermion:

   \documentclass[12pt]{article}
   
   \usepackage{amsfonts,amsmath,amssymb,amscd,amstext,mathabx,latexsym}
   \usepackage{textcomp,multicol,enumitem}
   \usepackage{tikz,tikz-feynman,contour}
   
   \begin{document}
   
   \tikzfeynmanset{
   every fermion={black},
   every photon={blue},
   every blob={/tikz/fill=blue!30,/tikz/inner sep=2pt},
   }
   
   \begin{tikzpicture}
     \begin{feynman}[every blob={/tikz/fill=blue!30,/tikz/inner sep=2pt}]
       \feynmandiagram [horizontal=a to b] {
         a -- [fermion] b [blob] -- [fermion] c};
     \end{feynman}
   \end{tikzpicture}
   
   \end{document}
   

   Compiled with LuaLaTeX, this gives me the following:

   

2. When I place the vertices horizontally, the blob does not appear:

   \documentclass[12pt]{article}
   
   \usepackage{amsfonts,amsmath,amssymb,amscd,amstext,mathabx,latexsym}
   \usepackage{textcomp,multicol,enumitem}
   \usepackage{tikz,tikz-feynman,contour}
   
   \begin{document}
   
   \tikzfeynmanset{
   every fermion={black},
   every photon={blue},
   every blob={/tikz/fill=blue!30,/tikz/inner sep=2pt},
   }
   
   \begin{tikzpicture}
   \begin{feynman}
   \vertex (a1) {\(e\)}; 
   \vertex[right=1.2cm of a1,blob] (a2) ;
   \vertex[right=1.2cm of a2] (a3) {\(e\)};
   
   \diagram* {
   (a1) -- [fermion] (a2) [blob] -- [fermion] (a3), };
   \end{feynman}
   \end{tikzpicture}
   
   \end{document}
   

   Compiled with LuaLaTeX, this gives me the following:

   

I don't understand where is the problem, I checked every step of the instructions given in J. Ellis' tutorial 2016.

Any idea of what might go wrong on my PC or LaTeX file?

Answer 1

Using the option layered layout allows you to set multiple vertices on the same horizontal alignment.

It may be worth noting, you don't need to load tikz because tikz-feynman already does so for you. It's also generally best not to load a \feynmandiagram inside a \begin{feynman}...\end{feynman}, because that can lead to some strange spacing behavior as noted in a previous question.

\documentclass{article}

\usepackage{tikz-feynman}

\begin{document}

\tikzfeynmanset{
  every fermion={black},
  every photon={blue},
  every blob={/tikz/fill=blue!30,/tikz/inner sep=2pt},
}

\begin{tikzpicture}
  \begin{feynman}
    \diagram [horizontal=a to b,layered layout] {
      a[particle=$e$] -- [fermion] b [blob] -- [fermion] c[particle=$e$]
    };
  \end{feynman}
\end{tikzpicture}

\end{document}