费曼图中线的平衡长度（feynmp）

Question

如何才能使费曼图更加对称？我希望“光子/Z 传播子”更短，如果可能的话，在我的图的最右侧留出更多空间，即“超电荷”和“Ws”衰变的地方。

我曾尝试寻找其工作原理phantom，fmffreez但我不知道它能如何帮助我。

% DIRECT PRODUCTION OF CHARGINO/NEUTRALINO
\unitlength=1mm
\begin{figure}
\begin{center}
\begin{fmffile}{wz}
\begin{fmfgraph*}(90,30)
 % INCOMING + OUTGOING PARTICLES
  \fmfleft{d1,d2,e1,d3,d4,e2,d5,d6} % incoming particles, from below
  \fmfright{l1,n,X01,X02,q,qbar} % outgoing particles, from below
  \fmf{phantom}{d1,v0}
  \fmf{phantom}{d2,v0}
  \fmf{phantom}{d3,v0}
  \fmf{phantom}{d4,v0}
  \fmf{phantom}{d5,v0}
  \fmf{phantom}{d6,v0}
  \fmf{plain}{e1,v0} % incoming electron
  \fmf{plain}{e2,v0} % incoming positron
  \fmf{photon,label=$\gamma/Z$}{v0,v1}

  % DRAW STUFF
  \fmf{photon,label=\textcolor{red} {$\tilde{\chi}_1^{\pm}$},label.side=right,foreground=red}{v1,v2} % chargino, lower
  \fmf{photon,label=\textcolor{red}{$\tilde{\chi}_1^{\pm}$},label.side=left,foreground=red}{v1,v3}  % chargino, upper
  \fmf{photon,label=$W^{\pm}$,label.side=right,label.dist=0.3}{v2,v4} % lower W
  \fmf{photon,label=$W^{\pm}$,label.side=left,label.dist=0.2}{v3,v5} % upper W
  % decay of upper W
  \fmf{plain}{l1,v4,n}
  % decay of lower W
  \fmf{plain}{q,v5,qbar}
  % neutralinos in final state
  \fmf{photon,foreground=red}{v2,X01} % upper
  \fmf{photon,foreground=red}{v3,X02} % lower
  % additional lines for SUSY particles
  \fmf{plain,foreground=red}{v3,X02}
  \fmf{plain,foreground=red}{v1,v3}
  \fmf{plain,foreground=red}{v1,v2}
  \fmf{plain,foreground=red}{v2,X01}

% LABELLING
 \fmflabel{$e^+$}{e2} % incoming proton (first, from top)
 \fmflabel{$e^-$}{e1} % incoming proton (second)
 \fmflabel{$\bar{q}$}{qbar} % lepton in final state (first) in Z decay
 \fmflabel{$q$}{q} %  lepton in final state (second) in Z decay
 \fmflabel{$\nu$}{n} % neutralino in final state from W decay
 \fmflabel{$\ell^{\pm}$}{l1} % lepton in final state from W decay
 \fmflabel{\textcolor{red}{$\tilde{\chi}_1^0$}}{X01} % final state neutralino
 \fmflabel{\textcolor{red}{$\tilde{\chi}_1^0$}}{X02} % final state neutralino
\end{fmfgraph*}
\end{fmffile}
\end{center}
\hspace{1cm}
\end{figure}

Answer 1

给长光子添加一些张力。

\fmf{photon,tension=3,label=$\gamma/Z$}{v0,v1}

在我的系统上看起来正确。

你画的每条线的默认张力为 1，重量为单位。由于右侧有太多额外的线，它们会拉伸中间的光子。增加光子的张力可以平衡右侧的拉力。

Answer 2

尽管您提到使用feynmf/feynmp，但我会提供使用另一个包的答案：钛钾费曼（加拿大运输安全局）。如果您需要使用，请不要觉得有义务接受这个答案feynmf/feynmp。

使用默认的底层算法放置所有顶点，可以这样做：

\feynmandiagram [horizontal=z1 to z2] {
  %% Incoming electrons
  e1 [particle=\(e^{-}\)]
    -- [fermion] z1
    -- [fermion] e2 [particle=\(e^{+}\)],

  %% gamma/Z propagator
  z1 -- [boson, edge label=\(\gamma / Z\)] z2,

  %% Supersymmetric particles
  {[edges={plain, boson}]
    z2 -- [edge label'=\(\tilde \chi_{1}^{\pm}\)] x1
       -- x3 [particle=\(\tilde \chi_{1}^{0}\)],
    z2 -- [edge label=\(\tilde \chi_{1}^{\pm}\)] x2
       -- x4 [particle=\(\tilde \chi_{1}^{0}\)],
  },
  %% We don't want the \chi to be too far apart
  x1 -- [draw=none] x2,

  %% W decaying hadronically
  x1 -- [boson, edge label'=\(W^{\pm}\)] w1,
  q11 [particle=\(\overline q\)] -- [fermion] w1 -- [fermion] q12 [particle=\(q\)],
  x2 -- [boson, edge label=\(W^{\pm}\)] w2,
  q21 [particle=\(\overline q\)] -- [fermion] w2 -- [fermion] q22 [particle=\(q\)],

  %% Finally, the algorithms wants to fan out the particles as much as possible,
  %% so to counter that we tie them together
  {[edges={draw=none}]
    q11 -- q12 -- x3 -- x4 -- q21 -- q22,
  },
};

这可能适合你，但如果你想要更精细的控制，那么你必须使用手动或相对放置顶点。代码变得有点复杂，但并不难以管理：

\begin{tikzpicture}
  \begin{feynman}
    %% e e -> Z
    \vertex (z1);
    \vertex [above left=1.5cm and 1cm of z1] (e1) {\(e^{-}\)};
    \vertex [below left=1.5cm and 1cm of z1] (e2) {\(e^{+}\)};
    \vertex [right=2cm of z1] (z2);

    %% Z -> X X
    \vertex [above right=1cm of z2] (x1);
    \vertex [below right=1cm of z2] (x2);

    %% We now add the decays of the supersymmetric particles
    \vertex [right=2cm of x1] (x3) {\(\tilde \chi_{1}^{0}\)};
    \vertex [above right=1cm of x1] (w1);
    \vertex [right=1cm of w1] (q11) {\(\overline q\)};
    \vertex [above right=0.5cm and 1cm of w1] (q12) {\(q\)};
    %% Repeat with the second particle
    \vertex [right=2cm of x2] (x4) {\(\tilde \chi_{1}^{0}\)};
    \vertex [below right=1cm of x2] (w2);
    \vertex [right=1cm of w2] (q21) {\(\overline q\)};
    \vertex [below right=0.5cm and 1cm of w2] (q22) {\(q\)};

    %% Now connect the dots (literally)
    \diagram* {
      (e1) -- [fermion] (z1) -- [fermion] (e2),
      (z1) -- [boson, edge label=\(\gamma / Z\)] (z2),

      {[edges={plain, boson}]
        (z2) -- [edge label=\(\tilde \chi_{1}^{\pm}\)] (x1) -- (x3),
        (z2) -- [edge label'=\(\tilde \chi_{1}^{\pm}\)] (x2) -- (x4),
      },

      (x1) -- [boson, edge label=\(W^{\pm}\)] (w1),
      (x2) -- [boson, edge label'=\(W^{\pm}\)] (w2),

      (q11) -- [fermion] (w1) -- [fermion] (q12),
      (q21) -- [fermion] (w2) -- [fermion] (q22),
    };
  \end{feynman}
\end{tikzpicture}

对于每个代码，都包含在：

\documentclass[tikz]{standalone}

\usepackage[compat=1.1.0]{tikz-feynman}

\begin{document}
%% <code above>
\end{document}