ψ-Lithium-7: A Retentive Solution to the Cosmological Lithium Problem. Alternative Title: ψ-Lithium-7 — Retentive Cosmology of Post-Equilibrium Isotopic Distributions

The cosmological lithium-7 discrepancy has persisted for decades as a structural anomaly in Big Bang Nucleosynthesis (BBN). Standard models predict a Li-7 abundance nearly three times higher than that observed in stellar spectra, and no nuclear or astrophysical correction has resolved the gap. This paper introduces the ψ-retentive Lagrangian, a theoretical framework in which lithium-7 is interpreted not as a depletion artifact but as a retentive node (Ξ) — a stable locus where difference (Δψ) between theoretical symmetry and empirical reality is preserved. Numerical simulations demonstrate that the ψ-retentive field reproduces the observed Li-7 under-abundance (Δψ ≈ 3.4 × 10⁻¹⁰) while maintaining negligible ψ-energy density. The model predicts subtle ψ-correlations with deuterium isotopic variation, offering a testable extension for post-equilibrium cosmology. By reframing the lithium anomaly as a manifestation of universal retention, this work establishes a quantitative link between cosmological asymmetry, information preservation, and the ψ-Architecture of difference.