feynlag.operators

Derivative operators and momentum-space substitution.

Ported from bsm-calc/models/DLRSM1: symbolic_tools.PartialMu / momentum and feynman_rules.D_linear (here with the field set passed explicitly instead of read from module globals — the original recursion also silently dropped the fields argument, fixed here).

Momentum convention (see CONVENTIONS.md): ∂_μ φ → i p(φ) φ where p(φ) is the (symbolic) momentum associated with the leg carrying field φ. Covariant derivatives Dmu and field strengths arrive in Phase 3.

Module Attributes

momentum

Symbolic momentum carried by a field: momentum(phi) prints as p(phi).

Functions

D_linear(expr, fields)	Distribute ∂_μ over sums and products (linearity + Leibniz rule).
Dmu(field[, gauge_groups])	Covariant derivative of a field: column Matrix over components.
expand_derivatives(expr, fields)	Rewrite every PartialMu(<product>) in expr via the Leibniz rule.
to_momentum_space(expr, fields)	Full derivative pipeline: Leibniz-expand then ∂_μ φ → i p(φ) φ.

Classes

PartialMu(arg)

The differential operator ∂_μ acting on a field expression.