feynlag.pheno.calculator.partial_width¶ feynlag.pheno.calculator.partial_width(vertex, M, m1, m2, color_factor=1, symmetry_factor=1)[source]¶ Γ = S · N_c · ⟨|M|²⟩ · √λ(M²,m₁²,m₂²)/(16πM³). Returns 0 when the channel is closed (M < m₁+m₂) and that is decidable; an undecidable symbolic comparison keeps the channel.