feynman-tikz

name	feynman-tikz
description	Render Feynman diagrams in TikZ-Feynman for direct LaTeX embedding — standalone or inline

Feynman TikZ

Generate TikZ-Feynman code for Feynman diagrams that can be directly embedded in LaTeX documents. Supports both standalone compilation and inline use within papers.

Workflow

1. Parse the diagram request: Identify the process, topology (s/t/u-channel, loop), and any special features (blobs, effective vertices, cut lines).

2. Choose the rendering approach:

   • \feynmandiagram — Simple inline diagrams with automatic layout
   • \begin{feynman} environment — Full control over vertex placement
   • Use the environment for any diagram with more than 4 external legs or loops

3. Generate the TikZ-Feynman code:

   • Define vertices with meaningful names
   • Connect with appropriate edge styles:
     • fermion / anti fermion — solid arrow
     • photon — wavy line
     • gluon — coiled line (use half left/half right for loops)
     • charged boson — wavy with arrow
     • scalar / charged scalar — dashed line
     • ghost — dotted line
   • Label external particles and momenta
   • Add momentum arrows where needed

4. Provide both formats:

   • Inline: Ready to paste into a \begin{figure} environment
   • Standalone: Complete document that compiles to a PDF/PNG

5. Compilation note: TikZ-Feynman requires LuaLaTeX for automatic vertex placement. Include a fallback with manual placement for pdfLaTeX compatibility.

Example

Input: "Draw the one-loop gluon self-energy diagram (gluon bubble)"

Output:

\feynmandiagram [horizontal=a to b] {
  i [particle=$g$] -- [gluon, momentum=$k$] a
    -- [gluon, half left, momentum=$k{-}q$] b
    -- [gluon, half left, momentum=$q$] a,
  b -- [gluon, momentum=$k$] f [particle=$g$],
};

Style

Reference: docs/design-system.md — the canonical source of truth for all visual rules.

Palette: Ink-only (Palette C). Include the style package in the preamble:

\usepackage{hephaestus-tikz}   % from styles/hephaestus-tikz.sty

Key rules:

• All lines default to hepInk (#1a1a1a) at 1.0pt. Use the every accent style for the boson or propagator being discussed (draws in hepAccent).
• Vertex style: hep vertex (4pt filled black circle). Apply only at interaction vertices.
• Label styles: hep label for external legs (italic, gray, 2pt inner sep), hep propagator label for internal lines (italic, accent color, midway).
• Use \hepsetaccent{steel} to switch to Slate Precision context if the diagram accompanies an exclusion contour.
• Square aspect ratio. Generous padding — external legs at least 30% of diagram width.
• Use \begin{feynman}[layered layout, horizontal=a to b] inside a tikzpicture for standard diagrams.

Validation

• Verify that all vertices connect correctly
• Check that the diagram compiles without errors
• Confirm particle flow arrows are consistent with charge conservation