feynlag.vertices.vertex

Vertex objects and the closed Lorentz-structure catalog.

The vertex catalog is CLOSED: SSS, SSSS, VSS, VVS, VVSS, VVV, VVVV, FFS, FFV, and FFFF (four-fermion, dim-6 effective operators). Classification is rule-based on the spin content of the legs; anything outside the catalog raises loudly (no silent drops). Each catalog entry carries the UFO lorentz.py structure name used at export.

FFFF cannot be reconstructed from the sorted spin letters alone — the four letters don’t say which fermion pairs into which Dirac chain. A caller that builds a Vertex for a four-fermion operator must record the chain pairing in Vertex.meta['pairing'] (the two (bar, gamma, field) subkeys produced by extract_fermion_vertices()).

VVVV has the same shape of problem for a different reason: it needs three couplings, one per Lorentz structure, tied to a specific leg ordering (a permutation mixes them). Vertex.from_structures() records those in Vertex.meta['structures']; Vertex.coupling is zero for such a vertex.

Module Attributes

LORENTZ_CATALOG

vertex type → UFO lorentz structure name(s)

Functions

classify_spins(field_tuple, spin_map)

Vertex type string from the spins of the legs.

Classes

Vertex(particles, coupling[, vertex_type, meta])

One Feynman vertex.