# Double wiggly line with arrow using feynmf

Please, could you help me to draw a double wiggly line with an arrow? I can drow a single woggly line with arrow using this code

  \begin{fmffile}{vertex}
\fmfcmd{%
style_def wiggly_arrow expr p =
cdraw (wiggly p);
shrink (1);
cfill (arrow p);
endshrink;
enddef;}
\begin{fmfgraph*}(100,60)
\fmfleft{i1}
\fmfright{o1,o2}
\fmflabel{$g$}{v1}
\fmf{wiggly_arrow,label=$\hat{a}$,l.side=left}{i1,v1}
\fmf{fermion,label=$\sigma$,l.side=right}{v1,o1}
\fmf{dashes_arrow,label=$\hat{D}$,l.side=left}{v1,o2}
\fmfdotn{v}{1}
\end{fmfgraph*}
\end{fmffile}


When I just change "wiggly" by "dbl_wiggly", this code no longer works.

I don't really care for the look of this but the following does produce a double wiggly line with an arrowhead superimposed near the center:

\begin{fmffile}{vertex}
\fmfcmd{%
style_def dbl_wiggly_arrow expr p =
draw_double (wiggly p);
shrink (1);
cfill (arrow p);
endshrink;
enddef;}
\begin{fmfgraph*}(100,60)
\fmfleft{i1}
\fmfright{o1,o2}
\fmflabel{$g$}{v1}
\fmf{dbl_wiggly_arrow,label=$\hat{a}$,l.side=left}{i1,v1}
\fmf{fermion,label=$\sigma$,l.side=right}{v1,o1}
\fmf{dashes_arrow,label=$\hat{D}$,l.side=left}{v1,o2}
\fmfdotn{v}{1}
\end{fmfgraph*}
\end{fmffile}


Note the draw_double (wiggly p) in place of the more obvious cdraw (dbl_wiggly p).

• Dear @Dan, thank you very much! This works well! – user2891657 Nov 28 '16 at 23:05