We introduce a derivative-based diagnostic to probe the redshift evolution of cosmic structure growth. While standard ΛCDM cosmology predicts a smooth and monotonic decline of the observable fσ₈(z), we test for deviations in the form of a flattening or reduced slope in its derivative: D(z) = d(fσ₈)/dz We define a quantitative flattening condition over a redshift interval Δz: |D(z)| < ε where ε is determined by observational uncertainties. Such a flattening would directly indicate a departure from purely monotonic growth models. We show that this behavior arises naturally in the presence of a retentive structural contribution, leading to a saturation regime in which growth is no longer governed solely by expansion dynamics. The proposed test provides a minimal and falsifiable distinction between smooth dissipative models and structurally constrained alternatives. The diagnostic can be directly applied to current and upcoming datasets, including DES, Euclid, and LSST.
Logacheva Yulia (Sat,) studied this question.