[Tex/LaTex] tikz-feynman package – horizontal alignment of graphs

feynmantikz-feynman

I would like to draw three of the following Feynman diagram side by side:

Here is the code to generate the above the Feynman diagram:

\begin{center}
\begin{tikzpicture}
    \begin{feynman}
        \vertex (i1) {\(p_{1}\)};
        \vertex [above right=of i1] (a) {\(\mu\)};
        \vertex [      right=of a ] (b) {\(\nu\)};
        \vertex [      above=of b ] (c) {\(\rho\)};
        \vertex [      left =of c ] (d) {\(\sigma\)};
        \vertex [      below=of d ] (a);
        \vertex [below right=of b ] (i2) {\(p_{2}\)};
        \vertex [above right=of c ] (f2) {\(k_{2}\)};
        \vertex [above  left=of d ] (f1) {\(k_{1}\)};
        \diagram* {
            (i1) -- [photon] (a) -- [fermion, edge label'=\(q-p_{2}\)] (b) -- [fermion, edge label'=\(q\)] (c) -- [fermion, edge label'=\(q-k_{2}\)] (d) -- [fermion, edge label'=\(q-p_{1}-p_{2}\)] (a),
            (b) -- [photon] (i2),
            (c) -- [photon] (f2),
            (d) -- [photon] (f1),
        };
    \end{feynman}
\end{tikzpicture}
\end{center}

How do I generate the three diagrams side by side?

Also, how do I move the indices to a side so that each pair of three lines join at a vertex?

Best Answer

To generate the diagrams side-by-side, you just add them one after each other:

\documentclass[tikz]{article}

\usepackage[compat=1.1.0]{tikz-feynman}

\begin{document}
\begin{center}
  \begin{tikzpicture}[baseline=(current bounding box.center)]
    \begin{feynman}
      \vertex (i1) {\(p_{1}\)};
      \vertex [above right=of i1] (a);
      \vertex [      right=of a ] (b);
      \vertex [      above=of b ] (c);
      \vertex [      left =of c ] (d);
      \vertex [      below=of d ] (a);
      \vertex [below right=of b ] (i2) {\(p_{2}\)};
      \vertex [above right=of c ] (f2) {\(k_{2}\)};
      \vertex [above  left=of d ] (f1) {\(k_{1}\)};
      \diagram* {
        (i1) -- [photon] (a) -- [fermion, edge label'=\(q-p_{2}\)] (b) -- [fermion, edge label'=\(q\)] (c) -- [fermion, edge label'=\(q-k_{2}\)] (d) -- [fermion, edge label'=\(q-p_{1}-p_{2}\)] (a),
        (b) -- [photon] (i2),
        (c) -- [photon] (f2),
        (d) -- [photon] (f1),
      };
    \end{feynman}
  \end{tikzpicture}
  %
  \begin{tikzpicture}[baseline=(current bounding box.center)]
    \def\leglength{1}
    \begin{feynman}
      \vertex[blob] (m) at (0, 0) {};
      \vertex (a) at (-\leglength,-\leglength);
      \vertex (b) at ( \leglength,-\leglength);
      \vertex (c) at (-\leglength, \leglength);
      \vertex (d) at ( \leglength, \leglength);
      \diagram* {
        (a) -- [photon] (m) -- [photon] (c),
        (b) -- [photon] (m) -- [photon] (d),
      };
    \end{feynman}
  \end{tikzpicture}
  %
  \feynmandiagram [baseline=(current bounding box.center), horizontal=a to b, node distance=1.5cm] {
    a -- [photon] o [blob] -- [photon] b,
    c -- [photon] o        -- [photon] d,
  };
\end{center}
\end{document}

Note that I put % on the lines in between as I want to prevent LaTeX from thinking there should be a newline. Also, baseline is used to adjust the vertical alignment of the diagrams.

Related Solutions

[Tex/LaTex] TikZ-Feynman: layers and alignment

Good to see TikZ-Feynman being put to good use!

So, the main issue here is that the layered layout (unlike most other algorithms) takes into account the order in which vertices are specified. In particular, it has a notion of layers and with:

a -- b

This tells it that a is on the layer above b and is distinct from b -- a. So in your example, you have

g [particle=\(\nu\)] 
  -- f 
  -- h [particle=\(\bar{\nu}\)]

and as a result, the neutrino at g is on the layer above f which itself is a layer above the antineutrino at h, hence why the neutrino is awkwardly sitting at the bottom of the central fermion line.

Now as to make it more compact, you can use sibling distance and layer distance to adjust the separation between vertices on the same layer or across layers respectively.

With all this, two of the three dot-points above are addressed:

\documentclass{standalone}
\usepackage[compat=1.1.0]{tikz-feynman}

 \begin{document}

 \feynmandiagram[layered layout, vertical=a to c, sibling distance=1cm] {
   g1 [particle=\(g\)]
     -- [gluon] a
     -- [fermion] t1 [particle=\(t\)],
  { [same layer]
    c -- [fermion, edge label=\(t\)] b
      -- [fermion, edge label=\(t\)] a},
   b  -- [boson, edge label=\(Z\)] n2,
   n2 -- [anti fermion] n1 [particle=\(\overline \nu\)],
   n2 -- [fermion] n3 [particle=\(\nu\)],
   g2 [particle=\(g\)]
      -- [gluon] c
      -- [anti fermion] t2 [particle=\(\overline t\)],
 };
\end{document}

Finally, if you want even finer control on everything, then the algorithm won't be able to meet all your needs and you'll have to adjust things manually. You can see some example of this being done at:

How to draw Feynman diagram for Majorana particles?

Tikz-Feynman: Multiple arrows on one fermion line and alignment (0vββ)

[Tex/LaTex] Propagator loop in Feynman diagram using tikz-feynman package

The issue here is that the algorithm that TikZ-Feynman (CTAN) uses in order to place the vertices doesn't work well if it only has a straight line because the difference in the optimization between a mostly-straight and a fully-straight line are quite small.

This can be easily fixed by using an alternative layout algorithm, such as the layered layout in this case:

%% luatex85 is only necesary to fix a bug in standalone
\RequirePackage{luatex85}
\documentclass{standalone}

\usepackage[compat=1.1.0]{tikz-feynman}

\begin{document}
\feynmandiagram [horizontal=a to b, layered layout] {
  a -- b [dot] -- [out=135, in=45, loop, min distance=3cm] b -- c,
};
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] TikZ-Feynman: layers and alignment

[Tex/LaTex] Propagator loop in Feynman diagram using tikz-feynman package

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