Aligning propagators on feynmp

Question

I want to align the propagators that go from the circle to the vertices p_3 and p_4

Here is my MWE:

\documentclass[amsmath,amssymb,aps,12pt,eqsecnum]{revtex4}    
\usepackage[a4paper]{geometry}    
\linespread{1}      
\usepackage{slashed}          
\usepackage{simplewick}        
\usepackage{feynmp-auto}        
\usepackage[pdftex]{graphicx}        
\usepackage{textcomp}        
\usepackage{gensymb}         
\begin{document}     
\begin{fmffile}{counterterms3}        
    \begin{fmfgraph*}(100,100)    
        \fmfbottom{i0,i1,i2,i3}    
        \fmftop{o1,o2}    
        \fmf{plain}{i1,v2}    
        \fmf{plain}{i2,v1}    
        \fmf{plain,left}{v2,v3}    
        \fmf{plain,right}{v1,v3}    
        \fmf{plain}{v3,o1}    
        \fmf{plain}{v3,o2}    
        \fmfv{label=$p_1$}{i1}    
        \fmfv{label=$p_2$}{i2}    
        \fmfv{label=$p_3$}{o1}    
        \fmfv{label=$p_4$}{o2}    
        \fmffreeze    
        \fmf{phantom}{v1,v2}    
        \fmf{plain,left}{v1,v2}    
        \fmf{plain,left}{v2,v1}   
        \fmf{dot}{v3}    
    \end{fmfgraph*}    
\end{fmffile}    
\end{document}

As you can see, the propagators from the circle go horizontal at the vertex with the dot, rather than going in the same direction as the propagators which lead to p_3 and p_4

Answer 1

You may make these curves parallel by playing with left and right.

\begin{fmfgraph*}(100,100)    
    \fmfbottom{i0,i1,i2,i3}    
    \fmftop{o1,o2}    
    \fmf{plain}{i1,v2}    
    \fmf{plain}{i2,v1}    
    \fmf{phantom,left}{v2,v3}    
    \fmf{phantom,right}{v1,v3}    
    \fmf{plain}{v3,o1}    
    \fmf{plain}{v3,o2}    
    \fmfv{label=$p_1$}{i1}    
    \fmfv{label=$p_2$}{i2}    
    \fmfv{label=$p_3$}{o1}    
    \fmfv{label=$p_4$}{o2}    
    \fmffreeze    
    \fmf{plain,left=1.45}{v2,v3}    
    \fmf{plain,right=1.45}{v1,v3}    
    \fmf{phantom}{v1,v2}    
    \fmf{plain,left}{v1,v2}    
    \fmf{plain,left}{v2,v1}   
    \fmf{dot}{v3}    
\end{fmfgraph*}