调整 tikz 树的行为以适应费曼图

Question

我正在使用 tikz 绘制费曼图，并且对调整以下代码的行为有一些疑问。

\documentclass[a4paper,12pt]{article}
\usepackage{tikz}
\usetikzlibrary{calc,matrix,arrows,decorations.pathmorphing,decorations.markings,trees}
\begin{document}
     \tikzset{
         photon/.style={decorate, decoration={snake}, draw=red},
             particle/.style={draw=blue,solid, postaction={decorate},
         decoration={markings,mark=at position .5 with {\arrow[draw=blue]{>}}}},
         antiparticle/.style={draw=blue,solid, postaction={decorate},
             decoration={markings,mark=at position .5 with {\arrow[draw=blue]{<}}}},
         wboson/.style={draw=black,dashed}
     }
     \begin{tikzpicture}[
         thick,
         % Set the overall layout of the tree
         level/.style={level distance=2.0cm},
         level 2/.style={sibling distance=3.5cm},
     ]
     \coordinate
         child[grow=left]{
             edge from parent [wboson]
             child {
                 edge from parent [particle]
                 node [above] {$d^r_L$}
             }
             child {
                 edge from parent [antiparticle]
                 node [below] {$u^r_L$}
             }
             node [above=3pt] {$W^+$}
          }
         % I have to insert a dummy child to get the tree to grow
         % correctly to the right.
         child[grow=right, level distance=0pt] {
             child { }
             child {
                 edge from parent [particle]
                 node [above] {$\nu_L$}
             }
         }
         child[grow=left, level distance=0pt]{
             child {
                 edge from parent [particle]
                 node [above] {$\overline{e^-_L}$}
             }
             child { }
         };
     \end{tikzpicture}
\end{document}

1）如何从图片中去除黑色实线，以便只保留虚线和四条蓝线？

2）如何调整蓝线之间的角度，以便最右边的两条蓝线描述一个锐角，而完全不增加级别/兄弟距离？

谢谢你的时间

Answer 1

1）从手册 p222 中，child {edge from parent[draw=none] }向虚拟节点添加选项以消除黑线。

2)level distance和sibling distance属性对每个子树都生效一次。就您的代码而言，您无法执行要执行的操作，因为您的树并不均匀。如果我没有看错的话，它从右顶点“开始”，然后向左移动到 wboson，然后分裂为反粒子/粒子对，向右回溯并产生最右边的蓝线，然后再次回溯并产生中间的蓝线。这不是很简单 :)

另一种方法是从标签处开始树W^+，以零级别分离“向下”生长，以便树左右生长，并从那里散开：

 \path
     [grow=down, level distance=0pt,sibling distance=1cm]
     coordinate [above, label={$W^+$}] 
     child [grow=left, level distance=1cm]{
       edge from parent [wboson]
       % Add [level distance=whatever, sibling distance=whatever] if you'd like
       child {
         node [above] {$d^r_L$}
         edge from parent [particle]
       }
       child {
         node [below] {$u^r_L$}
         edge from parent [antiparticle]
       }
     }
     child [grow=right, level distance=1cm, sibling distance=1cm] {
       edge from parent [wboson]
       [grow=up] % Add level distance=whatever, sibling distance=whatever here
       child { 
         node [above] {$\nu_L$}
         edge from parent [particle]
       }
       child {
         node [above] {$\overline{e^-_L}$}
         edge from parent [particle]
       }
     };       

（您可以根据需要调整级别距离）这种方法的另一个优点是您不再有任何虚拟线。稍有缺点是您必须将路径W^+“分成两半”，但您可以重新获得预期的不变量，即树的每个节点都沿一个统一的方向生长。