# feynlag

Tree-level Feynman rules from Beyond-Standard-Model Lagrangians, in pure
[SymPy](https://sympy.org).

You declare particle fields with their gauge and discrete-symmetry
representations, write the Lagrangian explicitly with library building
blocks (`Dmu`, `dag`, `Bilinear`), and `feynlag` takes it from there:
gauge/discrete invariance and hermiticity checks, electroweak symmetry
breaking, mass-matrix diagonalization, rotation to the physical basis,
vertex extraction across the closed Lorentz catalog, and export to LaTeX
tables or UFO (MadGraph and friends). The `feynlag.pheno` module turns the
resulting Feynman rules into decay widths, branching ratios and tree-level
2→2 cross sections.

The centerpiece of this site is the **Algorithms Manual**: one chapter per
pipeline stage, with the physics statement, the algorithm as it's actually
coded, a full derivation of the key results, the design gotchas that shaped
the implementation, and the pinned test that fixes each physical result.

::::{grid} 2
:gutter: 3

:::{grid-item-card} Getting Started
:link: getting-started
:link-type: doc
Install, and the quick tour from the README.
:::

:::{grid-item-card} Algorithms Manual
:link: manual/pipeline
:link-type: doc
Full derivations, stage by stage: declare → write → check → break → diagonalize → extract → export.
:::

:::{grid-item-card} Tutorials
:link: tutorials/index
:link-type: doc
Executed notebooks walking the SM and its extensions end to end, plus decays and scattering.
:::

:::{grid-item-card} Examples
:link: examples
:link-type: doc
Annotated gallery of the worked models in `examples/`.
:::

:::{grid-item-card} Conventions
:link: conventions
:link-type: doc
Every sign, metric, and normalization choice, pinned by tests.
:::

:::{grid-item-card} API Reference
:link: api/index
:link-type: doc
Auto-generated reference for every public module.
:::
::::

```{toctree}
:hidden:
:maxdepth: 2

getting-started
manual/pipeline
manual/declaration
manual/lagrangian
manual/invariance
manual/ssb
manual/masses
manual/diagonalization
manual/vertices
manual/export
manual/verification
manual/suggest
manual/anomalies
manual/charges
manual/flavor
manual/decays
manual/decays_roadmap
manual/scattering_roadmap
tutorials/index
examples
benchmark
roadmap
conventions
api/index
```