# Drawing Feynman Diagrams with feynMP

I'm trying to draw the higgs decay to two gluon diagram

but I want gluons to go straight right and take top quark label in the middle of the loop on the line. my script is as follows:

\usepackage{feynmp-auto}
\begin{fmffile}{h_gg}
\begin{fmfgraph*}(150,150)
\fmfleft{i1}
\fmfright{o1,o2}

\fmflabel{$h$}{i1}
\fmflabel{$g$}{o1}
\fmflabel{$g$}{o2}

\fmf{dashes_arrow}{i1,v1}
\fmf{quark,label=$t$}{v1,v2}
\fmf{quark,label=$t$}{v2,v3}
\fmf{quark,label=$t$}{v3,v1}
\fmf{gluon}{v2,o1}
\fmf{gluon}{v3,o2}
\fmf{phantom}{o1,o2}
\fmfdot{v1,v2,v3}
\end{fmfgraph*}
\end{fmffile}


Please note that the big dot is just because of me its nothing to do with latex. Also is there a possibility that I can change the angle between outputs in a LO decay diagram, for instance, higgs to bbbar which can be;

\begin{fmffile}{two_body}
\begin{fmfgraph*}(70,70)
\fmfleft{i1}
\fmfright{o1,o2}
\fmflabel{$h$}{i1}
\fmflabel{$b,c,\tau$}{o1}
\fmflabel{$\bar{b} ,\bar{b} ,\bar{\tau}$}{o2}
\fmf{dashes_arrow}{i1,v1}
\fmf{quark}{v1,o1}
\fmf{quark}{v1,o2}
\end{fmfgraph*}
\end{fmffile}


Thanks.

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Please move the second part to a new question. –  Thruston May 31 '14 at 18:49

You want to add some dummy nodes on the right so that o1 and o2 are nearer the middle, then freeze the automatic layout with fmffreeze and finally push v2 and v3 apart with fmfshift. Like this:

\documentclass{article}
\usepackage{feynmp-auto}
\begin{document}
\begin{fmffile}{h_gg}
\begin{fmfgraph*}(150,150)
\fmfleft{i1}
\fmfright{d1,d2,o1,o2,d3,d4}
\fmflabel{$h$}{i1}
\fmflabel{$g$}{o1}
\fmflabel{$g$}{o2}
\fmf{dashes_arrow,tension=2}{i1,v1}
\fmf{quark,label=$t$,label.side=right}{v1,v2}
\fmf{quark,label=$t$}{v2,v3}
\fmf{quark,label=$t$}{v3,v1}
\fmf{gluon}{v2,o1}
\fmf{gluon}{v3,o2}
\fmfdot{v1,v2,v3}
\fmffreeze
\fmfshift{11down}{v2}
\fmfshift{11up}{v3}
\end{fmfgraph*}
\end{fmffile}
\end{document}


Notice I've added a couple of other small tweaks to make it a bit neater. Adding tension=2 to the dashed arrow makes it balance the two gluons better. And I've pushed one of the quark labels to the other side of the arrow.

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this puts t labels inside the loops is there any chance that I can take the labels out? –  jackaraz May 31 '14 at 18:51
run it twice, so that the labels get re-positioned as in my diagram –  Thruston May 31 '14 at 18:52
yes I did but different numbers for up and down or for \begin{fmfgraph*}(150,150) changes the places of the labels is there any function to fix them? –  jackaraz May 31 '14 at 18:59
@jackaraz run it twice after making changes... –  cfr May 31 '14 at 21:09