% !TEX program = pdflatexmk
% !TEX parameter = -shell-escape
% Author: Izaak Neutelings (September 24)
% Instructions: To compile via command line, run the following twice
%   pdflatex -shell-escape extract/anomalous_momentum$TAG.tex
\documentclass[11pt,border=4pt]{standalone}
\usepackage{feynmp-auto}
\usepackage{xcolor}
\definecolor{collep}{rgb}{.1,.6,.1} % lepton (green)
\begin{document}
\begin{fmffile}{feyngraph}
  \fmfframe(2,2)(6,2){ % padding (L,T)(R,B)
  \begin{fmfgraph*}(90,90) % canvas (W,H)
    % line style
    \fmfset{wiggly_len}{12} % boson wavelength
    \fmfset{wiggly_slope}{65} % boson slope of waves
    % external vertices
    \fmfbottom{f2,f1}
    \fmftop{g}
    % main process
    \fmf{boson,t=1.2}{g,v} % photon
    \fmf{plain,f=(.1,,.6,,.1),t=1}{v1,v,v2} % internal lepton
    \fmf{fermion,f=(.1,,.6,,.1)}{v1,f1} % incoming lepton
    \fmf{fermion,f=(.1,,.6,,.1)}{f2,v2} % outgoing lepton
    % virtual photon
    \fmffreeze
    \fmf{boson,label=$\gamma$,l.s=left}{v1,v2}
    % labels
    \fmfv{l.a=-50,l.d=8,l=$\gamma$}{g}
    \fmfv{l.a=-25,l=\color{collep}$\tau$}{f1}
    \fmfv{l.a=-155,l=\color{collep}$\tau$}{f2}
  \end{fmfgraph*}
  } % close \fmfframe
\end{fmffile}
\end{document}