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I'm trying to draw of the vacuum diagrams in Yukawa theory with tikz-feynman, but I'm having some trouble doing the fermion loops that start and end at the same point. Here is my current attempt:

\documentclass{article}
\usepackage{tikz}
\usepackage[compat=1.1.0]{tikz-feynman}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
    \setlength\PreviewBorder{1em}

\begin{document}
\begin{tikzpicture}[transform shape, >=Stealth]
    \begin{feynman}
        \vertex (z);
        \vertex [left=0.5cm of z] (z1);
        \vertex [right=0.75cm of z] (w);
        \vertex [right=0.5cm of w] (w1);
        \node at (w)[circle,fill,inner sep=1pt]{};
        \node at (z)[circle,fill,inner sep=1pt]{};
        \diagram* {
            (w1) -- [<-, half left, looseness=1.75] (w) -- [half left, looseness=1.75] (w1),
            (z1) -- [half left, looseness=1.75] (z) -- [->, half left, looseness=1.75] (z1),
            (z) -- [scalar] (w),
        };
    \end{feynman}
\end{tikzpicture}
\end{document}

It yields the following result:

Attempt at solution

Which has distorted circles, ill-positioned arrows and uses arrows which are similar, but clearly different, from the ones that appear in the fermion propagators. I would like to get a result more similar to this (which is Figure 6a of this file):

Desired output

If possible, I'd like for the arrows on the bubbles to be the same ones that appear in the fermion propagators (even if it means redefining the arrows on the propagators). It is ok if it is not possible, but I'd like something which at least resembles the propagator arrows.

1 Answer 1

4

You probably want to bend the arrows.

\documentclass{article}
\usepackage{tikz}
\usepackage[compat=1.1.0]{tikz-feynman}
\usetikzlibrary{bending}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{1em}

\begin{document}
\begin{tikzpicture}[transform shape, >={Stealth[bend]}]
    \begin{feynman}
        \vertex (z);
        \vertex [left=0.5cm of z] (z1);
        \vertex [right=0.75cm of z] (w);
        \vertex [right=0.5cm of w] (w1);
        \node at (w)[circle,fill,inner sep=1pt]{};
        \node at (z)[circle,fill,inner sep=1pt]{};
        \diagram* {
            (w1) -- [postaction={draw,<-}, out=-90,in=-90, looseness=1.75] (w) -- 
            [half left, looseness=1.75] (w1),
            (z1) -- [half left, looseness=1.75] (z) -- 
            [postaction={draw,->}, out=-90,in=-90, looseness=1.75] (z1),
            (z) -- [scalar] (w),
        };
    \end{feynman}
\end{tikzpicture}
\end{document}

enter image description here

You do not really use tikz-feynman here, so you could draw perfect circles and just use TikZ. This can be uploaded to the arXiv.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{arrows.meta,bending,positioning}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{1em}

\begin{document}
\begin{tikzpicture}[>={Stealth[bend]}]
        \coordinate (z);
        \coordinate[right=0.75cm of z] (w);
        \node at (w)[circle,fill,inner sep=1pt]{};
        \node at (z)[circle,fill,inner sep=1pt]{};
        \draw (z) arc[start angle=0,end angle=360,radius=0.25]
         (w) arc[start angle=-180,end angle=180,radius=0.25];
        \draw[->] (z) arc[start angle=0,end angle=200,radius=0.25];
        \draw[->] (w) arc[start angle=180,end angle=380,radius=0.25];
        \draw[dashed] (z) -- (w);
\end{tikzpicture}

\begin{tikzpicture}[>={Triangle[bend,width=3pt,length=5pt]}]
        \coordinate (z);
        \coordinate[right=0.75cm of z] (w);
        \node at (w)[circle,fill,inner sep=1pt]{};
        \node at (z)[circle,fill,inner sep=1pt]{};
        \draw (z) arc[start angle=0,end angle=360,radius=0.25]
         (w) arc[start angle=-180,end angle=180,radius=0.25];
        \draw[->] (z) arc[start angle=0,end angle=200,radius=0.25];
        \draw[->] (w) arc[start angle=180,end angle=380,radius=0.25];
        \draw[dashed] (z) -- (w);
\end{tikzpicture}
\end{document}

enter image description here

3
  • What I had in mind originally was shifting the arrows up a bit (so the base was where the tip is) and preferably changing the arrow design, but I actually really liked this solution Commented Jun 1, 2020 at 6:39
  • 1
    @NíckolasAlves Please have a look at the second part of the answer. I also prefer the arrow heads in the middle.
    – user194703
    Commented Jun 1, 2020 at 6:44
  • That's precisely what I had in mind! Commented Jun 1, 2020 at 6:47

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