IV.T170 — p-n Mass NLO: C.5 Two-Sector Formula Structural Derivation

C.5 two-sector formula (m_n-m_p)/m_n = (3/16)·√3·ι_τ^5 - (3/20)·α·ι_τ^2 at +28 ppm. Structural derivation of both coefficients: 3/16=N_c/2⁴ (Dirac spinor-loop); 3/20=N_c/(4·W₃(4)) (EM crossing × Window). C.3 NLO also τ-effective at +5 ppm. First structural derivation of the EM coefficient from Window Universality.