Regime-Dependent Structural Residuals in ΛCDM: A Minimal Extension from Structural Saturation

We propose a minimal extension to the standard ΛCDM model based on the emergence of regime-dependent structural residuals in the matter power spectrum. Instead of introducing new fields or modifying gravity, we interpret observed deviations as a structural consequence of the breakdown of the linear perturbative regime. We introduce the Regime-Dependent Structural Saturation (RDSS) mechanism, under which nonlinear mode coupling induces a localized enhancement of power around a characteristic scale k*. This effect is modeled as a smooth residual term applied to the ΛCDM power spectrum. The framework preserves the large-scale success of ΛCDM while naturally accounting for small-scale discrepancies and high-redshift observations, including recent results from the James Webb Space Telescope.