[Tex/LaTex] Feynman diagram using feynmf – keeping lines straight after vertex, keeping line flat

diagramsfeynmf

\documentclass[a4paper,11pt]{report}
\usepackage{feynmp}
\usepackage[pdftex]{graphicx}
\DeclareGraphicsRule{*}{mps}{*}{}
\begin{document}
\begin{figure}
\label{fig:ele_int_conv}
\centering
\parbox{0.5\textwidth}{
\begin{fmffile}{nonres}
\begin{fmfgraph*}(250,125)
\fmfleft{i1,i2}
\fmfright{o1,o2,o3,o4}
\fmf{fermion,lab=$q$}{i1,v1}
\fmf{fermion,lab=$\bar{q}$}{i2,v1}
\fmf{boson,lab=$Z$}{v1,v2}
\fmf{fermion,lab=$\mu^+$}{v2,v3,o1}
\fmf{boson,lab=$\gamma^*$}{v3,v4}
\fmf{fermion,lab=$e^+$ (missed)}{v4,o2}
\fmf{fermion,lab=$e^-$}{v4,o3}
\fmf{fermion,lab=$\mu^-$}{v2,o4}

\end{fmfgraph*}
\end{fmffile}

Minimal working example produces this which is generally fine, but I would like to make the central "Z" line exactly horizontal, and I would like the \mu^+ line to be straight, and only have one label.

Best Answer

Basically what you need here are:

phantom particles (to define the skeleton you want)
\fmffreeze (to freeze the current shape before drawing further)

In the solution below, I've also used tension to make some of the lines shorter and label.side to stop the labels overlapping. These are slightly hack-y so you might want to play around with them. In particular, I moved the Z->mu mu vertex a bit to the left to leave space for everything that is happening on the right hand side. You may prefer another solution.

NB. I tested this with feynmf rather than feynmp.

\documentclass[a4paper,11pt]{report}
\usepackage{feynmf}
\usepackage[pdftex]{graphicx}
\DeclareGraphicsRule{*}{mf}{*}{}

\begin{document}
\begin{figure}
\label{fig:ele_int_conv}
\centering
\parbox{0.5\textwidth}{
  \begin{fmffile}{nonres}
  \begin{fmfgraph*}(250,125)
    \fmfleft{i1,i2}
    \fmfright{o1,o2,o3,o4}
    \fmf{fermion,label=$q$,tension=2}{i1,v1}
    \fmf{fermion,label=$\bar{q}$,tension=2}{i2,v1}
    \fmf{boson,label=$Z$,tension=2}{v1,v2}
    \fmf{fermion,label=$\mu^-$}{v2,o4}
    \fmf{phantom}{v2,o1}
    \fmffreeze
    \fmf{phantom}{v2,v3}
    \fmf{phantom}{v2,v3,o1}
    \fmffreeze
    \fmf{fermion,label=$\mu^+$,label.side=right}{v2,o1}
    \fmf{boson,label=$\gamma^*$,label.side=left}{v3,v4}
    \fmf{fermion,label=$e^+$ (missed),label.side=left,label.dist=1}{v4,o2}
    \fmf{fermion,label=$e^-$,label.side=left}{v4,o3}
  \end{fmfgraph*}
  \end{fmffile}
}
\end{figure}
\end{document}

Related Solutions

[Tex/LaTex] Draw single-vertex Feynman diagram

You need to define an external vertex also for the blob, with something like \fmfbottom{b}.

Using feynmp-auto you can avoid running metapost. Run pdflatex twice.

\documentclass{article}
\usepackage{feynmp-auto}
\unitlength=1mm
\begin{document}
\begin{fmffile}{DistributionScattering}
  \begin{fmfgraph*}(40,25)
    % Define two vertices on the left, but only `i2' will be actually used.
    \fmfleft{i1,i2}
    % The same on the right.
    \fmfright{o1,o2}
    % Define the vertex for the blob.
    \fmfbottom{b}
    \fmf{fermion,label=\(k_{\textup{i}}\),label.side=left}{i2,v1}
    \fmf{fermion,label=\(k_{\textup{f}}\),label.side=left}{v1,o2}
    \fmf{photon}{v1,b} \fmfblob{.15w}{b}
    % Labels on vertices.
    \fmflabel{e\(^{-}\)}{i2} \fmflabel{e\(^{-}\)}{o2}
  \end{fmfgraph*}
\end{fmffile}
\end{document}

This is the result:

You need to define two vertices on both sides because the diagram would be too flat otherwise. With this code

\begin{fmffile}{DistributionScattering}
  \begin{fmfgraph*}(40,25)
    \fmfleft{i2}
    \fmfright{o2}
    \fmfbottom{b}
    \fmf{fermion,label=\(k_{\textup{i}}\),label.side=left}{i2,v1}
    \fmf{fermion,label=\(k_{\textup{f}}\),label.side=left}{v1,o2}
    \fmf{photon}{v1,b}
    \fmfblob{.15w}{b}
    \fmflabel{e\(^{-}\)}{i2}
    \fmflabel{e\(^{-}\)}{o2}
  \end{fmfgraph*}
\end{fmffile}

the result would be

This example should help you understand why it's better using dummy vertices on both sides:

\begin{fmffile}{DistributionScattering}
  \begin{fmfgraph*}(40,25)
    \fmfleft{i1,i2}
    \fmfright{o1,o2}
    \fmfbottom{b}
    \fmf{fermion}{i2,v1,o2}
    \fmf{photon}{v1,b}
    \fmflabel{i1}{i1}
    \fmflabel{i2}{i2}
    \fmflabel{o1}{o1}
    \fmflabel{o2}{o2}
    \fmflabel{b}{b}
  \end{fmfgraph*}
\end{fmffile}

[Tex/LaTex] Creating a Feynman loop diagram with feynmf

You are beyond the powers of the feynmf automatic layout routine so you need to use "immediate" mode to place your nodes.

However at that point, it usually become easier to draw the diagram directly in Metapost, using the feynmp macros. Like this:

enter image description here

prologues := 3;
outputtemplate := "%j%c.eps";
input feynmp;
beginfig(1);

path ring; ring = fullcircle scaled 78;
z1 = -z2 = 78 left; z3 = z2 rotated -24;

label.top(btex $\tau_j$ etex, point 2 of ring);
label.bot(btex $W^+$    etex, point 6 of ring);
label.top(btex $\nu_\tau$ etex, z1);
label.top(btex $\nu_\tau$ etex, z2);
label.rt(btex $\gamma_\mu$ etex, z3);

draw fermion z1 -- point 4 of ring;
draw fermion subpath(4,0) of ring;
draw fermion point 0 of ring -- z2;
draw_dashes_arrow subpath(4,8) of ring;
draw photon origin -- z3 cutbefore ring;

endfig;
end.

(Note that a fullcircle path has 8 points on it running anticlockwise from the 3 o'clock position.)

The interface is quite neat: feynmp defines a number of macros as path decorators, that take a path as the right argument and return a decorated path. For example fermion above. Unfortunately the set of decorators is not quite complete, so for the dashed arrow we have to call the draw_dashes_arrow macro directly. The only documentation that I've ever found is the Metapost source file, but fmfman.pdf is still useful.

Best Answer

Related Solutions

[Tex/LaTex] Draw single-vertex Feynman diagram

[Tex/LaTex] Creating a Feynman loop diagram with feynmf

Related Question