IV.R131 — Isospin splitting from polarity

The inequality m_d > m_u has a structural origin: the d-quark has eta-winding n = 1 mod 3 (chi_- dominant sector of the color group) while the u-quark has n = 2 mod 3 (complement class); chi_- dominant coupling to the strong vacuum Gamma_s^* through tightening produces higher effective mass, yielding isospin splitting delta_A ~ 1.293 MeV.