ψ-Retention Cosmology: A Scale-Invariant Structural Resolution of the Late-Time Growth Anomaly

Late-time cosmological data exhibit a universal, scale-independent suppression of structure growth with a fixed index γ = 0.639 ± 0.022, in tension with the General Relativity prediction (γ ≈ 0.55). This work develops a structural, retentive framework — ψ-Retention Cosmology — in which the observed growth index emerges as a mathematically defined infrared fixed point rather than a fitted parameter. The theory preserves strict scale invariance across linear and quasi-linear regimes, predicts a structural transition near z† ≈ 1.7, and provides a coherent explanation for multiple late-time anomalies without introducing new propagating degrees of freedom. The ψ-regime represents a post-dynamical saturation phase in which structural information remains finite as dynamical flux declines. The framework is presented here in a concise form, allowing forthcoming surveys (Planck PR4, DES Y6, Gold-2026, Euclid DR1) to further clarify its observational status.