% !TEX program = pdflatexmk
% !TEX parameter = -shell-escape
% Author: Izaak Neutelings (December 24)
% Instructions: To compile via command line, run the following twice
%   pdflatex -shell-escape extract/HNL$TAG.tex
\documentclass[11pt,border=4pt]{standalone}
\usepackage{feynmp-auto}
\usepackage{xcolor}
\usepackage{scalerel}
\newcommand{\mylbrace}[2]{\vspace{#2pt}\hspace{4pt}\scaleleftright[\dimexpr6pt+#1\dimexpr0.11pt]{\lbrace}{\rule[\dimexpr2pt-#1\dimexpr0.5pt]{-4pt}{#1pt}}{.}}
\newcommand{\myrbrace}[2]{\vspace{#2pt}\scaleleftright[\dimexpr6pt+#1\dimexpr0.11pt]{.}{\rule[\dimexpr2pt-#1\dimexpr0.5pt]{-4pt}{#1pt}}{\rbrace}\hspace{2pt}}
\definecolor{colHNL}{rgb}{.1,.5,.1} % HNL (green)
\begin{document}
\begin{fmffile}{feyngraph}
  \fmfframe(-5,13)(-17,16){ % padding (L,T)(R,B)
  \parbox{110pt}{\begin{fmfgraph*}(90,70) % canvas (W,H)
    % line style
    \fmfset{wiggly_len}{12} % boson wavelength
    \fmfset{wiggly_slope}{65} % boson slope of waves
    % external vertices
    \fmfleft{i2,i1}
    \fmfright{o2,o1}
    % main process
    \fmf{fermion}{i1,v,i2} % incoming particles
    \fmf{fermion}{v,o1} % outgoing particle
    \fmf{majorana,f=(.1,,.5,,.1)}{o2,v} % outgoing particle
    % labels
    \fmfv{l.d=5,l.a=155,l=q}{i1}
    \fmfv{l.d=4,l.a=-155,l=$\overline{\mathrm{q}}'$}{i2}
    \fmfv{l.d=4,l.a=25,l=$\ell^\mp$}{o1}
    \fmfv{l.d=4,l.a=-25,l=\color{colHNL} N$_\ell$}{o2}
    \fmfblob{20}{v}
  \end{fmfgraph*}}
  =\quad
  \parbox{120pt}{\begin{fmfgraph*}(110,65) % canvas (W,H)
    % external vertices
    \fmfleft{i2,i1}
    \fmfright{o2,o1}
    % main process
    \fmf{fermion}{i1,v1,i2} % incoming particles
    \fmf{boson,t=1,label=W$^\pm$,l.s=left}{v1,w2} % s-channel
    \fmf{fermion}{w2,o1} % outgoing particle
    \fmf{majorana,f=(.1,,.5,,.1)}{o2,w2} % outgoing particle
    % labels
    \fmfv{l.d=5,l.a=155,l=q}{i1}
    \fmfv{l.d=4,l.a=-155,l=$\overline{\mathrm{q}}'$}{i2}
    \fmfv{l.d=4,l.a=25,l=$\ell^\pm$}{o1}
    \fmfv{l.d=4,l.a=-25,l=\color{colHNL} N$_\ell$}{o2}
    \fmfdot{w2}
  \end{fmfgraph*}}
  +\quad
  \parbox{110pt}{\begin{fmfgraph*}(90,65) % canvas (W,H)
    % external vertices
    \fmfleft{i2,i1}
    \fmfright{o2,o1}
    % main process
    \fmf{fermion}{i1,v,i2} % incoming particles
    \fmf{fermion}{v,o1} % outgoing particle
    \fmf{majorana,f=(.1,,.5,,.1)}{o2,v} % outgoing particle
    % labels
    \fmfv{l.d=5,l.a=155,l=q}{i1}
    \fmfv{l.d=4,l.a=-155,l=$\overline{\mathrm{q}}'$}{i2}
    \fmfv{l.d=4,l.a=25,l=$\ell^\pm$}{o1}
    \fmfv{l.d=4,l.a=-25,l=\color{colHNL} N$_\ell$}{o2}
    \fmfdot{v}
  \end{fmfgraph*}}
  } % close \fmfframe
\end{fmffile}
\end{document}