Changing size and position of momentum arrows in LaTex Feynman diagrams

Question

I am making a Feynman diagram for Compton scattering in LaTeX. There are two diagrams actually. First one is ok. The code is:

\begin{tikzpicture}
  \begin{feynman}
    \diagram[horizontal=a to b] {
  i1 [particle=\(e^{-}\)] -- [fermion,momentum'=\(p_{i}\)] a -- [photon,reversed momentum'=\(k_{i}\)] f1 [particle=\(\gamma\)],
  a -- [fermion] b,
  i2 [particle=\(\gamma\)] -- [photon,reversed momentum'=\(k_{f}\)] b -- [fermion,momentum'=\(p_{f}\)] f2 [particle=\(e^{-}\)],
};
  \end{feynman}
\end{tikzpicture}

It results in:

Now, the second diagram did not end up well.

Code is:

\begin{tikzpicture}
  \begin{feynman}
    \diagram[horizontal=a to b] {
      i1 [particle=\(p_{i}\)]
         -- [fermion,momentum'=\(p_{i}\)] a
         -- [draw=none] f1 [particle=\(\gamma\)],
      a -- [fermion, edge label'=\( \)] b,
      f2 [particle=\(\gamma\)]
         --  [draw=none] b
         -- [fermion,momentum'=\(p_{f}\)] i2 [particle=\(p_{f}\)],
    };
    \diagram* {
      (a) -- [photon,momentum'=\(k_{f}\)] (f2),
      (f1) -- [photon,,momentum'=\(k_{i}\)] (b),
    };
  \end{feynman}
\end{tikzpicture}

It results in:

I want the photon momentum arrows to be above the photon lines, and shorter than they are now. I would also like them to be by the beginning of the photon line, not in the middle. This image shows approximately how I would want the diagram to look like. Red lines show where the arrows should be.

Any help is welcome! Thank you

Answer 1

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

\usepackage{tikz-feynman}

\begin{document}

\begin{tikzpicture}
  \begin{feynman}
    \diagram[horizontal=a to b] {
      i1 [particle=\(p_{i}\)]
         -- [fermion,momentum'=\(p_{i}\)] a
         -- [draw=none] f1 [particle=\(\gamma\)],
      a -- [fermion, edge label'=\( \)] b,
      f2 [particle=\(\gamma\)]
         --  [draw=none] b
         -- [fermion,momentum'=\(p_{f}\)] i2 [particle=\(p_{f}\)],
    };
    \diagram* {
      (a) -- [
                photon,
                momentum={[
                  arrow shorten=0.25, 
                  xshift=4mm,
                  yshift=2mm
                ]$k_{f}$}
              ] (f2),
      (f1) -- [
                photon,
                momentum={[
                  arrow shorten=0.25,
                  xshift=-4mm,
                  yshift=2mm
                ]$k_{i}$}
              ] (b),
    };
  \end{feynman}
\end{tikzpicture}

\end{document}