[Tex/LaTex] Drawing Feynman Diagrams with feynMP

Question

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.

Answer 1

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.