SM-4: Charged Lepton Masses from the K3 Spectral Theorem

Abstract: The K3 Spectral Theorem (SM-3) proves K = 2/3 as one constraint on three lepton masses, reducing three free parameters to two. The phase θ = 132.73 is extracted from PDG values. A structural theorem proves θ is undetermined within K3+SSV; its derivation is the principal open problem gating the electroweak series. Nature satisfies K = 2/3 to 11 ppm.