feynlag.vertices.bilinear.fermion_gauge_current¶
- feynlag.vertices.bilinear.fermion_gauge_current(fermion, flavor_index, gauge_groups=None, projector=None)[source]¶
Gauge-current terms of
i ψ̄ γ^μ D_μ ψ(the interaction part).With
D_μ = ∂_μ − i g T^a A^a_μ(CONVENTIONS.md), the interaction is+ g A^a_μ ψ̄_a γ^μ T^a_{ab} P ψ_b.- Parameters:
fermion – a
Fermion.flavor_index – flavor index symbol (the current is flavor diagonal).
gauge_groups – groups to include (default: all in
fermion.reps).projector – chiral projector; default from
fermion.chirality.
- Returns:
sum of
coupling × A × Bilinear(ψ̄_a, γ^μ P, ψ_b).- Return type:
SymPy expression