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I am curious to learn about Feynman diagrams, so I have started to read Richard Mattuck's book "A guide to Feynman Diagrams in the Many-Body problem".

One of the first diagrams that appears in this book he calls 'Open oyster diagram'. It describes two electrons interacting and exchanging positions and is depicted below (drawn with Inkscape):

So, the y axis has the meaning of time, while the x axis in this case has somehow the meaning of space.

Is there a reasonably simple way to create such a diagram with FeynMF?

In other words: How do I introduce a turn by 90 degrees at a certain vertex into the diagram shown below (created with FeynMF)?

FeynMF version

\documentclass{article}                                                                             
\usepackage{feynmp}
\DeclareGraphicsRule{*}{mps}{*}{}

\begin{document}

\begin{fmffile}{sp1}
\begin{fmfgraph*}(50,100)
    \fmfbottom{i1}
    \fmftop{o1}
    \fmf{fermion, label=$e$}{i1,v1}
    \fmf{fermion, right, tension=0.5}{v1,v2}
    \fmf{photon,label=$\gamma$, straight, tension=0.5}{v1,v2}
    \fmf{fermion, label=$e$ }{v2,o1}
\end{fmfgraph*}
\end{fmffile}                                                                                       

\end{document}

P.S. I realize that there are \fmffixed, \fmfforce and \fmfshift, but I didn't manage to come up with some nice combination that would work without having to adjust it for each new diagram.

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1 Answer 1

up vote 5 down vote accepted

\fmfforce does the trick. With feynmp-auto package you don't need to run metapost separately, just run latex twice.

\documentclass{article}
\usepackage{feynmp-auto}
\begin{document}

\begin{fmffile}{sp1}
  \begin{fmfgraph*}(50,100)
    \fmfforce{0,0}{i}
    \fmfforce{w,h}{o}
    \fmfforce{0,.5h}{v1}
    \fmfforce{w,.5h}{v2}
    \fmf{fermion, label=$e$, label.side=left}{i,v1}
    \fmf{fermion, right, tension=0.5}{v1,v2}
    \fmf{photon,label=$\gamma$, straight, tension=0.5}{v1,v2}
    \fmf{fermion, label=$e$ }{v2,o}
  \end{fmfgraph*}
\end{fmffile}

\end{document}

enter image description here

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+1 (and not only for using feynmp-auto). ;-) –  egreg Nov 28 '13 at 0:01

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