r_d × f_π = ℏc(1 − α): A Four-Constant Identity Linking Nuclear, Chiral, Quantum, and Electromagnetic Physics

Version 4.3 (5 April 2026): Errata update. Five corrections documented in Paper4_v43_ERRATA.pdf: (1) f_π precision claim corrected from 0.009% to 0.17 ± 0.15% (PDG 2024); (2) F_π vs f_π convention made explicit; (3) Author location corrected from Auckland, New Zealand to Warrnambool, Australia; (4) Equation (7) deviation corrected from 0.05% to 0.72%; (5) Proton charge radius updated to Maisenbacher et al. 2026 value (0.8406 ± 0.0015 fm). We report that the product of the deuteron charge radius r_d and the pion decay constant f_π satisfies r_d × f_π = ℏc(1 − α) to 0.17 ± 0.15%, where α = 1/137.036 is the fine structure constant. This four-constant identity connects nuclear structure (r_d), chiral symmetry…