Companion G: Neutron-Proton Mass Difference from 5D Y-Junction Topology

This companion paper presents the derivation of the neutron-proton mass difference ∆m = mn− mp = 1.293 MeV [BL] from 5D Y-junction topology in Elastic Diffusive Cosmology (EDC). What this paper does: Establishes (1) Z6 = Z3 × Z2 symmetry from ring oscillation topology [Dc], (2) the asymmetry parameter q = 1/3 from the half-Steiner configuration at δθ = 60◦ [Der], (3) the prefactor 1/6 from brane embedding geometry [Dc], and (4) connections to SU(3) color structure [I]. The result matches experiment to 0.6% accuracy. What this paper does NOT do: Derive the energy scale σr2e from first principles [OPEN], or prove the claim constitutes a genuine prediction rather than a calibrated consistency check. Calibration boundary: Two scale inputs enter this calculation: • V3 =−0.65 MeV [Cal] — tuned to match ∆m • σr2e = 70 MeV [BL] — external nuclear-scale input (not fitted here)