% !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$TAG.tex
\documentclass[11pt,border=4pt]{standalone}
\usepackage{feynmp-auto}
\usepackage{xcolor}
\definecolor{collep}{rgb}{.1,.6,.1} % lepton (green)
\definecolor{colvtx}{rgb}{.1,.1,.7} % vertex (dark blue)
\begin{document}
\begin{fmffile}{feyngraph}
  \fmfframe(2,2)(6,2){ % padding (L,T)(R,B)
  \begin{fmfgraph*}(80,85) % canvas (W,H)
    % line style
    \fmfset{wiggly_len}{12} % boson wavelength
    \fmfset{wiggly_slope}{65} % boson slope of waves
    % external vertices
    \fmfbottom{f2,f1}
    \fmftop{g}
    % main process
    \fmf{boson,t=1.2}{g,v} % photon
    \fmf{fermion,f=(.1,,.6,,.1)}{f2,v,f1} % lepton pair
    % labels
    \fmfv{decor.shape=circle,decor.filled=empty,decor.size=35,
       f=(.1,,.1,,.7),b=(.92,,.92,,.98),l=\color{colvtx}$g-2$,l.a=0,l.d=0}{v}
    \fmfv{l.a=-50,l.d=8,l=$\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}