[Tex/LaTex] How to adjust momentum arrows in TikZ-Feynman

tikz-feynman

I'm trying to create a Feynman-Diagra using the TikZ-Feynman package in Latex.

Is there anyway to adjust the position of the momentum arrows in TikZ? Right now the two momentum arrows of the photon lines overlap in the diagram and it doesn't look very nice. I would like to have the momentum arrows closer to the edge of the photon line. How can I do it?

\begin{tikzpicture}
    \begin{feynman}
    \diagram [baseline={(current bounding box.center)},vertical'=a to b] { 
      i1[particle=\(e^{-}\)] -- [anti fermion, rmomentum'={[arrow style=white,label style=black]\(p^\prime\)}] 
      a -- [draw=none] 
      f1[nudge=(-45:0.5cm),particle=\(\gamma\)], 
      a -- [anti fermion, rmomentum'={[arrow style=white,label style=black]\(p-k^\prime\)}] b,
      i2[particle=\(e^{-}\)] -- [fermion,rmomentum={[arrow style=white,label style=black]\(p\)}] 
      b -- [draw=none]
      f2[nudge=(45:0.5cm), particle=\(\gamma\)], };
      \diagram* {
        (a) -- [photon,rmomentum={[arrow shorten=0.15mm,arrow distance=3mm]\(k\)}] (f2),
        (b) -- [photon,momentum'={[arrow shorten=0.15mm,arrow distance=3mm]\(k\)}] (f1),
      };
    \end{feynman}
\end{tikzpicture}

Best Answer

I felt like procrastinating a bit, so here goes.

This is quite easy if you define the coordinates manually, with the \vertex macro. (See section 2.4.3 Manual placement in the manual, for a reference.)

\documentclass{article}
\usepackage[compat=1.1.0]{tikz-feynman}
\begin{document}   
\begin{tikzpicture}[
  arrowlabel/.style={
    /tikzfeynman/momentum/.cd, % means that the following keys are read from the /tikzfeynman/momentum family
    arrow shorten=#1,arrow distance=1.5mm
  },
  arrowlabel/.default=0.4
]
\begin{scope}[local bounding box=part A]
\begin{feynman}
% first define the coordinates
\vertex (a);
\vertex [right=of a] (b1);
\vertex [above=1cm of b1] (b2);
\vertex [above=1cm of b2] (b3);
\vertex [above=1cm of b3] (b4);
\vertex [right=of b4] (c);

% then draw connections
\diagram* {
  (a) -- [boson, momentum={[arrowlabel]$k$}] (b2),
  (b1) -- [fermion, edge label'=$p$]   (b2)
       -- [fermion, edge label'=$p+k$] (b3) 
       -- [fermion, edge label=$p'$]   (b4),
  (b3) -- [boson, momentum'={[arrowlabel]$k'$}] (c),
};
\end{feynman}
\end{scope}

\node [right=3mm of part A] (plus) {$+$};

\begin{scope}[local bounding box=part B, shift={([xshift=3mm]plus.east |- part A.south)}]
\begin{feynman}
\vertex (a);
\vertex [right=of a] (b1);
\vertex [above=1cm of b1] (b2);
\vertex [above=1cm of b2] (b3);
\vertex [above=1cm of b3] (b4);
\vertex [right=of b4] (c);

\diagram* {
  (a) -- [boson, momentum={[arrowlabel=0.42]$k$}] (b3),
  (b1) -- [fermion, edge label'=$p$]   (b2)
       -- [fermion]                    (b3) 
       -- [fermion, edge label=$p'$]   (b4),
  (b2) -- [boson, momentum'={[arrowlabel=0.42]$k'$}] (c),
};
\end{feynman}
\end{scope}
\end{tikzpicture}
\end{document}

Related Solutions

[Tex/LaTex] Installing Tikz-Feynman

Thanks for your interest in TikZ-Feynman. Since the package is available on CTAN, all you really need to do is make sure your distribution is up to date which is well described in this question.

If, for any reason, you can't update your distribution, you can still install the package in your local TEXMF tree. Firsty, you'll need to obtain the package files from either project page or CTAN. Next, you'll need to locate your local TEXMF tree, and there are instructions for that in other questions (Linux / Unix, Windows).

In the end, you should have all the files in:

$TEXMFHOME/tex/latex/tikz-feynman/<package files>

Note that TikZ-Feynman contains a few extra files in addition to the usual .cls files and just to be safe, you should copy them all.

[Tex/LaTex] Arrows in Feynman diagram

The momentum arrow should be, by default, 70% of the length of the initial path. This can change quite significantly if the path is quite curved, as it is here, but you can always rectify it with the arrow shorten key.

In particular, the momentum style allows for optional arguments as follows:

momentum={[<optional momentum styles>]<momentum label>}

I also noticed that you are manually placing labels to look like they are on the edge of certain propagators. You can actually automatically do this with edge label.

Here's the diagram with the momentum arrow shortened, and using edge label instead of manually placing nodes along edges:

\documentclass{article}

\usepackage{tikz-feynman}

\begin{document}
\begin{tikzpicture}[baseline=(current bounding box.north)]
  \begin{feynman}[small]
    \vertex (i1)  [particle=\(e^{-}\)];
    \vertex (start) at (-0.3,-0.2) {\(e^{-}\)};
    \vertex [above right=20pt of i1] (ii1);
    \vertex [above right=20pt of ii1] (v1);

    \vertex [above left=20pt of v1] (ii2);
    \vertex [above left=20pt of ii2] (i2) {\(e^{-}\)};

    \vertex [right=40pt of v1] (v2);

    \vertex [below right=20pt of v2] (ff1);
    \vertex [below right=20pt of ff1] (f1);
    \vertex [above right=20pt of v2] (ff2);
    \vertex [above right=20pt of ff2] (f2);

    \diagram* {
      (i1) -- [fermion, edge label'=\(p\)] (ii1)
           -- [fermion, edge label'=\(k\)] (v1),
      (ii1)-- [
               boson,
               momentum={[arrow shorten=0.25, arrow style=blue]},
               half left,
               blue] (ii2),
      (v1) -- [fermion, edge label'=\(k'\)] (ii2)
           -- [fermion, edge label'=\(p'\)] (i2),
      (v2) -- [boson, blue, momentum'={[arrow style=blue]\(q\)}, edge label=\(\gamma\)] (v1),
      (f1) -- [fermion,very thick] (v2)
           -- [fermion, very thick] (f2),
    };
  \end{feynman}
\end{tikzpicture}
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Installing Tikz-Feynman

[Tex/LaTex] Arrows in Feynman diagram

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