N15 — Helium-4 mass fraction $Y_p = 20/81$

N15: Prediction

Yp = 20/81.

$Y_p = 20/81 = 0.2469$ (V.T245). Orthodox: fitted from $η_B$. Observed: $0.2449 ± 0.0040$. Experiment: metal-poor HII regions. Timeline: ongoing.

Derivation Context

The fiber suppression is selective: it affects only $A ≥ 7$ nuclei (those requiring EM radiative capture across the full $τ^3$ geometry). Light nuclei with $A ≤ 4$ fit the stride-3 macrocell and are unaffected:

• $Y_p$ ($^4He$): unchanged (voxel packing geometry, independent of $^7Be$ production).
• $D/H$: unchanged (set by deuterium bottleneck, not by $^7Be$ channel).
• $^3He/H$: unchanged ($A = (τ^3) = 3$, fits macrocell).

No BBN products have $5 ≤ A ≤ 6$ (the mass gaps at $A = 5$ and $A = 8$ in nuclear physics prevent their formation). The $τ$ framework therefore resolves the lithium problem selectively—without disturbing the other successful BBN predictions. (Registry: V.T245, V.T246, Wave 25.)