IV.D08 — Spectral Fine Structure

Spectral fine structure constant α ≈ (8/15)·ι_τ⁴. Leading-order approximation from two τ² surface modes (exponent 4) and primorial factor 8/15 = 2³/(3·5). Gives α ≈ 0.00725, 1/α ≈ 137.9 (spectral approx, ~0.06% from experiment).