feynlag.pheno.amplitudes.ffv_squared¶

feynlag.pheno.amplitudes.ffv_squared(g_left, g_right, kin, vector_mass=None)[source]¶

V(P) → f(p₁) f̄(p₂) for Γ^μ = γ^μ(g_L P_L + g_R P_R).

Γ̄^μ = γ^μ(ḡ_L P_L + ḡ_R P_R) — a vector current is self-conjugate, the projector does not swap (see dirac_conjugate()). The same projector push-through as in ffs_squared() gives

chirality-diagonal: ½Tr[p̸₁γ^a p̸₂γ^b] (mass terms killed),
chirality-mixing: −m₁m₂ Tr[γ^aγ^b P_R] = −2m₁m₂ g^{ab},

contracted with Σ ε_a ε*_b and averaged over the parent’s three polarizations.