Examples

This section provides a collection of example Feynman diagrams demonstrating various features of tikz-feyn.

Basic Processes

Simple Fermion Propagator

\begin{tfeyn}
  \tfcol{i}
  \tfcol{o}
  \tf[f]{i,o}
\end{tfeyn}

Photon Propagator

\begin{tfeyn}
  \tfcol{i}
  \tfcol{o}
  \tf[p]{i,o}
\end{tfeyn}

Gluon Exchange

\begin{tfeyn}
  \tfcol{i}
  \tfcol{o}
  \tf[g]{i,o}
\end{tfeyn}

Scattering Processes

Electron-Positron Scattering (QED)

Basic s-channel process:

\begin{tfeyn}
  \tfcol{i1, i2}
  \tfcol{m1, m2}
  \tfcol{o1, o2}

  \tf[f]{i1, m1}    % e- incoming
  \tf[f]{i2, m2}    % e+ incoming
  \tf[p]{m1, m2}    % photon exchange
  \tf[f]{m1, o1}    % e- outgoing
  \tf[f]{m2, o2}    % e+ outgoing
\end{tfeyn}

With intermediate vertex:

\begin{tfeyn}
  \tfcol{i1, i2}
  \tfcol{o1, o2}

  \tf[f]{i1, v1, i2}[r]
  \tf[f]{o1, v2, o2}[l]
  \tf[p]{v1, v2}
\end{tfeyn}

Quark-Antiquark Annihilation

\begin{tfeyn}
  \tfcol{i1, i2}
  \tfcol{o1, o2}

  \tf[f]{i1, v, i2}[r]        % quark-antiquark annihilation
  \tf[g]{v, m}                % gluon
  \tf[f]{o1, m, o2}[l]        % quark pair creation
\end{tfeyn}

Compton Scattering

\begin{tfeyn}
  \tfcol{i1, i2}
  \tfcol{v1, v2}
  \tfcol{o1, o2}

  \tf[p]{i1, v1}     % incoming photon
  \tf[f]{i2, v1}     % incoming electron
  \tf[f]{v1, v2}     % electron propagator
  \tf[p]{v2, o1}     % outgoing photon
  \tf[f]{v2, o2}     % outgoing electron
\end{tfeyn}

Loop Diagrams

Fermion Self-Energy

\begin{tfeyn}
  \tfcol{i}
  \tfcol{o}

  \tf[f]{i, o}            % main propagator
  \tf[f, l]{i, o}         % fermion loop
  \tf[p, l]{i, o}         % photon connecting loop
\end{tfeyn}

Vertex Correction

One-loop vertex correction:

\begin{tfeyn}
  \tfcol{i1, i2}[1cm]
  \tfcol(0, 0.3cm){v1, v2}[0.3cm]
  \tfcol(0, -0.3cm){o1, o2}[1cm]

  \tf[f]{i2, v4, v2}
  \tf[f]{v2, v6, o2}
  \tf[p, l]{v4, v6}      % photon loop
  \tf[p]{v2, v1}
  \tf[f]{i1, v1, o1}
\end{tfeyn}

Vacuum Polarization

Photon with fermion loop:

\begin{tfeyn}
  \tfcol{i}
  \tfcol{o}

  \tf[p]{i, o}           % photon propagator
  \tf[f, l]{i, o}        % fermion loop
  \tf[f, l]{o, i}        % anti-fermion (opposite direction)
\end{tfeyn}

Higgs and Electroweak Processes

Higgs Production (Gluon Fusion)

\begin{tfeyn}
  \tfcol{i1, i2}
  \tfcol{o}

  \tf[g]{i1, v1, i2}[r]       % gluon fusion
  \tf[f, l]{v1, v2}           % top quark loop
  \tf[f, l]{v2, v3}
  \tf[f, l]{v3, v1}
  \tf[h]{v2, o}               % Higgs production
\end{tfeyn}

W Boson Exchange

\begin{tfeyn}
  \tfcol{i1, i2}
  \tfcol{m1, m2}
  \tfcol{o1, o2}

  \tf[f]{i1, m1}         % fermion
  \tf[f]{i2, m2}         % fermion
  \tf[w]{m1, m2}         % W boson exchange
  \tf[f]{m1, o1}         % fermion
  \tf[f]{m2, o2}         % fermion
\end{tfeyn}

Z Boson Production

\begin{tfeyn}
  \tfcol{i1, i2}
  \tfcol{o}

  \tf[f]{i1, v, i2}[r]   % fermion-antifermion annihilation
  \tf[z]{v, o}           % Z boson production
\end{tfeyn}

Box Diagrams

Four-Point Function

\begin{tfeyn}[2cm][1cm]
  \tfcol{i1, i2}
  \tfcol{m1, m2}
  \tfcol{m3, m4}
  \tfcol{o1, o2}

  \tf[f]{i1, m1}
  \tf[f]{i2, m2}
  \tf[f]{m1, m3}
  \tf[f]{m2, m4}
  \tf[p]{m1, m2}
  \tf[p]{m3, m4}
  \tf[f]{m3, o1}
  \tf[f]{m4, o2}
\end{tfeyn}

QCD Processes

Gluon Self-Energy

\begin{tfeyn}
  \tfcol{i}
  \tfcol{o}

  \tf[g]{i, o}
  \tf[g, l]{i, o}
  \tf[g, l]{o, i}
\end{tfeyn}

Three-Gluon Vertex

\begin{tfeyn}
  \tfcol{i1}
  \tfcol{i2}
  \tfcol{o}

  \tf[g]{i1, v}
  \tf[g]{i2, v}
  \tf[g]{v, o}
  \node[vertex] at (v) {};
\end{tfeyn}

Quark-Gluon Scattering

\begin{tfeyn}
  \tfcol{i1, i2}
  \tfcol{m1, m2}
  \tfcol{o1, o2}

  \tf[f]{i1, m1}     % quark
  \tf[g]{i2, m2}     % gluon
  \tf[g]{m1, m2}     % gluon exchange
  \tf[f]{m1, o1}     % quark
  \tf[g]{m2, o2}     % gluon
\end{tfeyn}

Advanced Techniques

Multiple Loops with Custom Looseness

\begin{tfeyn}
  \tfcol{i}[1cm]
  \tfcol{o}

  \tf[p, l, looseness=1]{i, o}
  \tf[p, l, looseness=1]{o, i}
  \tf[f, l]{i, o}
  \tf[f, l]{o, i}
\end{tfeyn}

Colored Diagrams for Presentations

\begin{tfeyn}
  \tfcol{i1, i2, i3}
  \tfcol{o1, o2, o3}

  \tf[f, red, thick]{i1, o1}
  \tf[p, blue, thick]{i2, o2}
  \tf[g, green!70!black, thick]{i3, o3}
\end{tfeyn}

Asymmetric Diagrams

Using position offsets for asymmetric layouts:

\begin{tfeyn}[1.5cm][0.8cm]
  \tfcol{i1, i2}[1cm]
  \tfcol(0, 0.5cm){m1}
  \tfcol(0, -0.5cm){o1, o2, o3}[0.5cm]

  \tf[f]{i1, m1}
  \tf[f]{i2, m1}
  \tf[f]{m1, o1}
  \tf[f]{m1, o2}
  \tf[f]{m1, o3}
\end{tfeyn}

Visible Interaction Vertices

\begin{tfeyn}
  \tfcol{i1, i2}
  \tfcol{m1, m2}
  \tfcol{o1, o2}

  \tf[f]{i1, m1}
  \tf[f]{i2, m2}
  \tf[p]{m1, m2}
  \tf[f]{m1, o1}
  \tf[f]{m2, o2}

  % Draw vertices
  \node[vertex] at (m1) {};
  \node[vertex] at (m2) {};
\end{tfeyn}

Inline Diagrams in Text

Simple Inline

The vertex
\begin{tfeynin}
  \tfcol{a, b}
  \tfcol{c}
  \tf[f]{a, c}
  \tf[f]{b, c}
  \tf[p]{c, d}
\end{tfeynin}
contributes to the amplitude.

In Equations

\begin{equation}
  \mathcal{M} =
  \begin{tfeynma}
    \tfcol{i1, i2}
    \tfcol{o1, o2}
    \tf[f]{i1, v1, i2}[r]
    \tf[f]{o1, v2, o2}[l]
    \tf[p]{v1, v2}
  \end{tfeynma}
  + \text{crossed terms}
\end{equation}

Custom Particle Types

Defining New Styles

\tikzset{
  scalar/.style={
    dashed,
    thick
  },
  s/.style={scalar},
  meson/.style={
    dash pattern=on 2pt off 2pt,
    line width=1pt
  },
  m/.style={meson}
}

\begin{tfeyn}
  \tfcol{i}
  \tfcol{o}
  \tf[s]{i, o}     % scalar particle
\end{tfeyn}

Tips and Tricks

Consistent Spacing

For diagrams in the same document, define consistent spacing:

\newcommand{\mydiagram}[1]{%
  \begin{tfeyn}[2cm][0.8cm][0.7cm][0.3cm]
    #1
  \end{tfeyn}%
}

\mydiagram{
  \tfcol{i}\tfcol{o}
  \tf[f]{i,o}
}

Reusable Components

Define common sub-diagrams:

\newcommand{\photonexchange}{%
  \tf[p]{m1, m2}
}

\begin{tfeyn}
  \tfcol{i1, i2}
  \tfcol{m1, m2}
  \tfcol{o1, o2}

  \tf[f]{i1, m1}
  \tf[f]{i2, m2}
  \photonexchange    % reusable component
  \tf[f]{m1, o1}
  \tf[f]{m2, o2}
\end{tfeyn}

Labels and Annotations

Add labels using TikZ nodes:

\begin{tfeyn}
  \tfcol{i1, i2}
  \tfcol{o1, o2}

  \tf[f]{i1, v1, i2}[r]
  \tf[f]{o1, v2, o2}[l]
  \tf[p]{v1, v2}

  \node[above] at (i1) {$e^-$};
  \node[below] at (i2) {$e^+$};
  \node[above] at (o1) {$e^-$};
  \node[below] at (o2) {$e^+$};
\end{tfeyn}