# tikz-feynman: edge labels

I would like to understand how can I label edges of diagrams as at this picture:

I assume that it possible to label vertices and than move each label, but I do not know how. Can anyone gives some suggestions?

What I tried: label each vertex

\begin{feynman}
\vertex (v1) {$$cl$$};
\vertex[right=0.5cm of v1] (v2) {$$cl$$};
\vertex[right=1cm of v2] (v3) {$$cl$$};
\vertex[right=0.5cm of v3] (v4) {$$cl$$};;
\diagram*{(v1)--(v2), (v2)--[half left](v3)--[half left](v2),(v3)--(v4)};
\end{feynman}


It is awful. Then, I have tried to label edges:

\begin{feynman}
\vertex (v1);
\vertex[right=0.5cm of v1] (v2);
\vertex[right=1cm of v2] (v3);
\vertex[right=0.5cm of v3] (v4);
\diagram*{(v1)--[edge label={$$cl \quad$$}](v2), (v2)--[half left,edge label={$$cl \quad cl$$}](v3)--[half left,edge label={$$cl \quad cl$$}](v2),(v3)--[edge label={$$\quad cl$$}](v4)};
\end{feynman}


It looks not so awful, but not perfect: labels are so far from edges.

• Could you please remove the green tick and give it to the user valerie? His answer is impeccable. Thank you. – Sebastiano Apr 25 at 14:26

Using hardcoded coordinates like \node(a) at (.6,-.5) {\small cl}; in tikz is a deadly sin, this will break as soon as you change the tiniest thing.

• to move the labels on the horizontal lines to the start and end of the lines, use near start and near end

• to move the labels around the circle closer to the line, reduce the inner sep

• don't use inline math to make multi-letter things italic

% !TeX TS-program = lualatex
\documentclass{article}
\usepackage{tikz-feynman}

\begin{document}

\begin{tikzpicture}
\begin{feynman}
\vertex (v1);
\vertex[right=0.5cm of v1] (v2);
\vertex[right=1cm of v2] (v3);
\vertex[right=0.5cm of v3] (v4);
\diagram*{
(v1)--[edge label={\textit{cl}},near start](v2),
(v3)--[edge label={\textit{cl}},near end](v4)
};
\end{feynman}
\end{tikzpicture}
\end{document}


Alternatively without any manual intervention, one can let tikz-feynman do it's job:

% !TeX TS-program = lualatex
\documentclass{article}
\usepackage{tikz-feynman}

\begin{document}

\begin{tikzpicture}[inner sep=2pt]
\itshape
\begin{feynman}
\diagram[horizontal=a to f,small]{
a--[edge label={cl},near start]b,
b -- [quarter right,edge label'={cl}]
c -- [quarter right,edge label'={cl}]
d -- [quarter right,edge label'={cl}]
e -- [quarter right,edge label'={cl}]
b,
d--[edge label={cl},near end]f
};
\end{feynman}
\end{tikzpicture}

\end{document}