Big Bang Nucleosynthesis (BBN) is the precision test of the early universe. While standard predictions for Deuterium and Helium-4 agree with observations to within 1%, the abundance of Lithium-7 is overestimated by a factor of 3 (a 5-sigma discrepancy). Standard solutions involving new particle physics often disrupt the delicate neutron-to-proton ratio, ruining the Helium-4 prediction. We propose a resolution based on a geometric extension of the Standard Model involving Bulk Lepton Leakage. We demonstrate that the energy scale for neutrino tunneling into the extra dimension is dynamically fixed by the binding energy of Deuterium (M* approx 2.22 MeV). We introduce a mechanism of Radion Stabilization via Stochastic Resonance: the continuous flux injection from the Bulk places the brane modulus in a metastable critical state. The baryonic phase transition (Deuterium formation) introduces a non-zero trace in the energy-momentum tensor, providing the coherent signal that triggers a vacuum selection event. This locks the barrier height to the nuclear binding scale. This "Deuterium Lock" acts as a high-pass energy filter: neutrino leakage is active only in the high-temperature phase (T > 2.22 MeV), suppressing Lithium precursors, but switches off exactly when nucleosynthesis begins, protecting the thermal bath required for Helium-4 stability. We present the modified Boltzmann equations and detailed reaction rate integrals, showing that this topological resonance offers a unique, surgical solution to the Lithium problem without fine-tuning.
Giovanni Frisina (Thu,) studied this question.