Xjyuk

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

beginfeynman
 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);
endfeynman

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

beginfeynman
 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);
 endfeynman

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

I have kept the same structure as you by eliminating your labels and I have inserted them manually using nodes.... (a) (b) .... with cartesian coordinates that have all small labels and are closer to the ellipse.

documentclass[tikz]article
usepackagetikz-feynman
tikzfeynmansetcompat=1.0.0
begindocument

begintikzpicture
beginfeynman
 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=](v2),
 (v2)--[half left,edge label=](v3)--[half left,edge label=](v2),
 (v3)--[edge label=](v4);
endfeynman
 node(a) at (.6,-.5) small cl;
 node(b) at (1.35,-.5) small cl;
 node(c) at (.6,.5) small cl;
 node(d) at (1.35,.5) small cl;
 node(e) at (-.11,.15) small cl;
 node(f) at (2.1,.15) small cl;
 endtikzpicture
enddocument

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
documentclassarticle
usepackagetikz-feynman

begindocument

begintikzpicture
beginfeynman
 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=textitcl,near start](v2), 
 (v2)--[half left,edge label=textitclquad cl,inner sep=1pt](v3)--[half left,edge label=textitclquad cl,inner sep=1pt](v2),
 (v3)--[edge label=textitcl,near end](v4)
 ;
 endfeynman
 endtikzpicture
enddocument

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

% !TeX TS-program = lualatex
documentclassarticle
usepackagetikz-feynman

begindocument

begintikzpicture[inner sep=2pt]
 itshape
 beginfeynman
 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
 ;
 endfeynman
endtikzpicture

enddocument