A Minimal Regime-Dependent Extension of ΛCDM via a Localized Structural Residual

We propose a minimal extension to the ΛCDM cosmological model through a localized structural residual term in the matter power spectrum. The model is constructed to remain negligible in regimes where ΛCDM successfully describes large-scale structure, while becoming relevant in regimes of excess small-scale power. We test the model against observational data from the Sloan Digital Sky Survey (SDSS) and find that it does not degrade the fit, remaining statistically indistinguishable from ΛCDM in standard regimes. This suggests that cosmological corrections may be regime-dependent rather than universal, providing a consistent framework for addressing anomalies observed in high-redshift data.