\section{Arrows and Labels}

In addition to the actual lines of a Feynman diagram one commonly desires
to include labels directly on the diagram, occasionally explanatory
text or equations, and quite frequently arrows indicating the flow of
momentum or some quantum number.  These are accommodated quite easily in 
\FEYNMAN.

\subsection{Arrows}

The command for drawing arrows is \bs drawarrow.
The syntax is similar to the \ddrawline\ command:

\begin{verbatim}

\drawarrow[<direction><configuration>]
          (<(x,y) co-ordinates of the arrow>)

\end{verbatim}
An arrowhead is produced at the specified (x,y) co-ordinates, generally
at the end or middle of a line.  The direction is one of the usual
compass point directions:

\begin{verbatim}

             \N   \NE   \E   \SE   \S   \SW   \W   \NW

\end{verbatim}
If \bs LDIR or \bs LINEDIRECTION is used instead then the direction of the
last drawn line will automatically be used (pre-supposing that a line has
been drawn in the current picture).  If the previous line was drawn by
the \ddrawvertex\ command (see next chapter) then the {\it initially specified}
vertex direction will be used.  The {\em configuration} is one of the
following:

\begin{verbatim}

                  \ATTIP                 \ATBASE

\end{verbatim}
These specify whether the co-ordinates which you've input refer to
the position of the {\bf base} of the arrow or the {\bf tip} of the
arrow.  Arrows may be drawn boldly if \bs thicklines is in operation.
The length of an arrow is given by the variable \bs arrowlength.
When an arrow is attached to the end of a line the \bs particlelengthx,y
are not altered (and neither is \bs gluonlengthx \etc) however the
variables \bs{\it boxlengthx} and \bs{\it boxlengthy}, mentioned in
subsection 2.10.2, assume a different meaning now.  The {\it tip} of the
arrow will always have co-ordinates (\bs~boxlengthx,\bs~boxlengthy),
whether it is drawn with \bs ATTIP or \bs ATBASE.  The following
examples should illustrate these features.

\begin{verbatim}
\documentstyle [12pt]{article}
\input FEYNMAN
\begin {document}
\bigphotons
\centerline{ARROWS using FEYNMAN.TEX}
\begin{picture}(10000,10000)(0,0)             % PICTURE 1
\drawline\fermion[\NE\REG](0,0)[8000] 
\drawarrow[\LDIR\ATTIP](\pmidx,\pmidy)
\drawline\fermion[\E\REG](\fermionbackx,\fermionbacky)[2000]
\drawline\fermion[\N\REG](\fermionfrontx,\fermionfronty)[2000]
\drawline\fermion[\W\REG](0,0)[2000]
\drawline\fermion[\S\REG](0,0)[2000]
\drawarrow[\S\ATBASE](0,-2000)
\drawarrow[\W\ATBASE](-2000,0)
\end{picture}
\hskip -0.4in
\begin{picture}(10000,10000)(0,0)             % PICTURE 2
\drawline\fermion[\SW\REG](0,0)[8000] 
\thicklines
\drawarrow[\SW\ATTIP](\pbackx,\pbacky)
\thinlines
\drawline\fermion[\W\REG](\fermionbackx,\fermionbacky)[2000]
\drawline\fermion[\S\REG](\fermionfrontx,\fermionfronty)[2000]
\drawline\fermion[\E\REG](0,0)[2000]
\drawline\fermion[\N\REG](0,0)[2000]
\drawarrow[\E\ATBASE](2000,0)
\drawarrow[\N\ATBASE](0,2000)
\end{picture}
\hskip -0.4in
\begin{picture}(10000,10000)(0,0)             % PICTURE 3 
\drawline\scalar[\SW\REG](0,0)[6] 
\drawarrow[\SW\ATTIP](\pbackx,\pbacky)
\drawline\fermion[\E\REG](0,0)[2000]
\drawline\fermion[\N\REG](0,0)[2000]
\drawarrow[\E\ATBASE](2000,0)
\drawarrow[\E\ATTIP](2000,0)
\drawarrow[\N\ATBASE](0,2000)
\drawarrow[\N\ATTIP](0,2000)
\drawline\fermion[\W\REG](\scalarbackx,\scalarbacky)[2000]
\drawline\fermion[\S\REG](\scalarbackx,\scalarbacky)[2000]
\drawarrow[\E\ATTIP](\scalarbackx,\scalarbacky)
\drawarrow[\N\ATTIP](\scalarbackx,\scalarbacky)
\end{picture}
\begin{picture}(10000,10000)(0,0)             % PICTURE 4 
\thicklines
\drawline\fermion[\NW\REG](0,0)[8000] 
\drawline\fermion[\W\REG](\fermionbackx,\fermionbacky)[2000]
\drawline\fermion[\N\REG](\fermionfrontx,\fermionfronty)[2000]
\drawarrow[\NW\ATBASE](-1000,1000)
\drawarrow[\NW\ATBASE](-2000,2000)
\drawarrow[\NW\ATBASE](-3000,3000)
\drawarrow[\NW\ATTIP](-4000,4000)
\drawarrow[\NW\ATTIP](-5000,5000)
\drawline\fermion[\E\REG](0,0)[2000]
\drawline\fermion[\S\REG](0,0)[2000]
\end{picture}
\begin{picture}(10000,10000)(0,0)             % PICTURE 5 
\drawline\photon[\E\REG](0,0)[8]
\drawline\fermion[\E\REG](\pbackx,\pbacky)[200]
\drawarrow[\E\ATBASE](\pbackx,\pbacky)
\drawline\fermion[\SW\REG](0,0)[2000]
\drawline\fermion[\NW\REG](0,0)[2000]
\end{picture}
\vskip 0.5in
\begin{picture}(10000,10000)(0,0)             % PICTURE 6 
\drawline\gluon[\E\REG](0,0)[8]
\drawarrow[\E\ATBASE](\pbackx,\pbacky)
\drawline\fermion[\SW\REG](0,0)[2000]
\drawline\fermion[\NW\REG](0,0)[2000]
\end{picture}
\hskip 0.42in
\begin{picture}(10000,10000)(0,0)             % PICTURE 7 
\drawline\photon[\SE\REG](0,0)[8] 
\drawarrow[\E\ATBASE](\pmidx,\pmidy)
\drawarrow[\E\ATBASE](\pbackx,\pbacky)
\drawline\fermion[\W\REG](0,0)[2000]
\drawline\fermion[\N\REG](0,0)[2000]
\end{picture}
\begin{picture}(10000,10000)(0,0)             % PICTURE 8 
\drawline\gluon[\SE\REG](0,0)[7] 
\drawarrow[\E\ATTIP](\pmidx,\pmidy)
\drawarrow[\S\ATBASE](\pbackx,\pbacky)
\drawline\fermion[\W\REG](0,0)[2000]
\drawline\fermion[\N\REG](0,0)[2000]
\end{picture}
\end{verbatim}
giving

\centerline{ARROWS using FEYNMAN.TEX}
\begin{picture}(10000,10000)(0,0)
\drawline\fermion[\NE\REG](0,0)[8000] 
\drawarrow[\LDIR\ATTIP](\pmidx,\pmidy)
\drawline\fermion[\E\REG](\fermionbackx,\fermionbacky)[2000]
\drawline\fermion[\N\REG](\fermionfrontx,\fermionfronty)[2000]
\global\advance\fermionfrontx by 400
\global\advance\fermionfronty by 400
\put(\fermionfrontx,\fermionfronty){{\scriptsize 1}}
\drawline\fermion[\W\REG](0,0)[2000]
\drawline\fermion[\S\REG](0,0)[2000]
\drawarrow[\S\ATBASE](0,-2000)
\drawarrow[\W\ATBASE](-2000,0)
\end{picture}
\hskip -0.4in
\begin{picture}(10000,10000)(0,0)
\drawline\fermion[\SW\REG](0,0)[8000] 
\thicklines
\drawarrow[\SW\ATTIP](\pbackx,\pbacky)
\thinlines
\drawline\fermion[\W\REG](\fermionbackx,\fermionbacky)[2000]
\drawline\fermion[\S\REG](\fermionfrontx,\fermionfronty)[2000]
\drawline\fermion[\E\REG](0,0)[2000]
\drawline\fermion[\N\REG](0,0)[2000]
\global\advance\fermionfrontx by 400
\global\advance\fermionfronty by 400
\put(\fermionfrontx,\fermionfronty){{\scriptsize 2}}
\drawarrow[\E\ATBASE](2000,0)
\drawarrow[\N\ATBASE](0,2000)
\end{picture}
\hskip -0.4in
\begin{picture}(10000,10000)(0,0)
\drawline\scalar[\SW\REG](0,0)[6] 
\drawarrow[\SW\ATTIP](\pbackx,\pbacky)
\drawline\fermion[\E\REG](0,0)[2000]
\drawline\fermion[\N\REG](0,0)[2000]
\global\advance\fermionfrontx by 400
\global\advance\fermionfronty by 400
\put(\fermionfrontx,\fermionfronty){{\scriptsize 3}}
\drawarrow[\E\ATBASE](2000,0)
\drawarrow[\E\ATTIP](2000,0)
\drawarrow[\N\ATBASE](0,2000)
\drawarrow[\N\ATTIP](0,2000)
\drawline\fermion[\W\REG](\scalarbackx,\scalarbacky)[2000]
\drawline\fermion[\S\REG](\scalarbackx,\scalarbacky)[2000]
\drawarrow[\E\ATTIP](\scalarbackx,\scalarbacky)
\drawarrow[\N\ATTIP](\scalarbackx,\scalarbacky)
\end{picture}
\begin{picture}(10000,10000)(0,0)
\thicklines
\drawline\fermion[\NW\REG](0,0)[8000] 
\global\advance\pmidy by 500
\put(\pmidx,\pmidy){{\scriptsize 4}}
\drawline\fermion[\W\REG](\fermionbackx,\fermionbacky)[2000]
\drawline\fermion[\N\REG](\fermionfrontx,\fermionfronty)[2000]
\drawarrow[\NW\ATBASE](-1000,1000)
\drawarrow[\NW\ATBASE](-2000,2000)
\drawarrow[\NW\ATBASE](-3000,3000)
\drawarrow[\NW\ATTIP](-4000,4000)
\drawarrow[\NW\ATTIP](-5000,5000)
\drawline\fermion[\E\REG](0,0)[2000]
\drawline\fermion[\S\REG](0,0)[2000]
\end{picture}
\begin{picture}(10000,10000)(0,0)
\drawline\photon[\E\REG](0,0)[8]
\global\advance\pmidx by -600
\global\advance\pmidy by 500
\put(\pmidx,\pmidy){{\scriptsize 5}}
\drawline\fermion[\E\REG](\pbackx,\pbacky)[200]
\drawarrow[\E\ATBASE](\pbackx,\pbacky)
\drawline\fermion[\SW\REG](0,0)[2000]
\drawline\fermion[\NW\REG](0,0)[2000]
\end{picture}
\vskip 0.5in
\begin{picture}(10000,10000)(0,0)
\drawline\gluon[\E\REG](0,0)[8]
\global\advance\pmidx by -200
\global\advance\pmidy by -2000
\put(\pmidx,\pmidy){{\scriptsize 6}}
\drawarrow[\E\ATBASE](\pbackx,\pbacky)
\drawline\fermion[\SW\REG](0,0)[2000]
\drawline\fermion[\NW\REG](0,0)[2000]
\end{picture}
\hskip 0.42in
\begin{picture}(10000,10000)(0,0)
\drawline\photon[\SE\REG](0,0)[8] 
\drawarrow[\E\ATBASE](\pmidx,\pmidy)
\drawarrow[\E\ATBASE](\pbackx,\pbacky)
\global\advance\pmidx by -200
\global\advance\pmidy by 500
\put(\pmidx,\pmidy){{\scriptsize 7}}
\drawline\fermion[\W\REG](0,0)[2000]
\drawline\fermion[\N\REG](0,0)[2000]
\end{picture}
\begin{picture}(10000,10000)(0,0)
\drawline\gluon[\SE\REG](0,0)[7] 
\drawarrow[\E\ATTIP](\pmidx,\pmidy)
\drawarrow[\S\ATBASE](\pbackx,\pbacky)
\global\advance\pmidx by 100
\global\advance\pmidy by 800
\put(\pmidx,\pmidy){{\scriptsize 8}}
\drawline\fermion[\W\REG](0,0)[2000]
\drawline\fermion[\N\REG](0,0)[2000]
\end{picture}
\hskip 0.41in
