We derive four parameter-free predictions for the PMNS leptonic mixing matrixfrom the level-5 metaplectic modular structure and the Rogers dilogarithmidentity at the golden-ratio point. The central invariant is the regulator: RM = 1 − 15·ln² (φ) /π² = 0. 6480636743378963580533. . . obtained from the Rogers identity L (φ⁻²) = π²/15 and verified to 100 decimalplaces by independent methods. Here φ = (1+√5) /2 is the golden ratio. Predictions (no free parameters after fixing φ): Comparison with NuFIT 6. 1 (Nov 2025, IC24+SK, Normal Ordering, www. nu-fit. org/? q=node/309): tan (θ₂₃) = 4·φ⁻³ → θ₂₃ = 43. 36° θ₂₃ = 43. 29° → |Δ| = 0. 07° tan (θ₁₂) = 12·φ⁻⁶ → θ₁₂ = 33. 80° θ₁₂ = 33. 76° → |Δ| = 0. 04° tan (θ₁₃) = RM·φ⁻³ → θ₁₃ = 8. 71° θ₁₃ = 8. 62° → |Δ| = 0. 09° δCP = 2π·RM → δCP = 233. 3° δCP = 212° (1σ: 176°–238°) → prediction within 1σ Comparison with the first JUNO measurement (59. 1 days, arXiv: 2511. 14593): sin²θ₁₂ = 0. 3092 ± 0. 0087 → θ₁₂ ≈ 33. 78° Prediction 33. 80° → |Δ| < 0. 02°. Cross-domain anchor: the same RM selects a unique geometric point in theRice-Mele condensed matter model at v = w/φ, via the Zak-phase identity γZak (Δ*) = 2π·RM, Δ* = 0. 44263293143506090037. . . certified by five independent procedures including interval arithmetic (Arb/Flint, certified width 7×10⁻³⁸). Deductive chain: M'₅ (level-5 metaplectic) → (A'₅ → A₅, RM) → (ρ₄, O₁₂, RM; modular weights 1, 2, 1) → (q₂₃, q₁₂, q₁₃, 2π·RM) → UMR → M_ν. Open element: explicit identification of the modular-form components ofΓ' (5) and Γ (5) realizing qᵢj as specific ratios. Numerical verificationcode (Python/mpmath and C/GCC) is included. Falsifiable commitments: (i) θ₂₃ remains in the lower octant (< 45°) ; (ii) δCP converges toward 233° as DUNE and Hyper-Kamiokande accumulatedata; (iii) precision improvements on θ₁₃ converge toward 8. 71°.
Sorin G. Mocanu (Fri,) studied this question.
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