ψ-Potential II: Retentional Transition and Structural Constraints in Late-Time Cosmology

This research note introduces the ψ-potential as a minimal structural term associated with the retention of already formed differences in late-time cosmology. Within this framework, cosmic evolution is interpreted as a transition from a dynamical regime of growth to a retentional regime characterized by suppressed structural variation and continued expansion. The work provides a minimal conceptual formulation of this transition, outlines consistency conditions for growth saturation, and presents an illustrative data fit consistent with observed values of the growth index and low-redshift behavior of fσ₈. The proposed framework does not modify gravity or expansion dynamics, but instead introduces a structural constraint on variation, offering a complementary perspective on late-time cosmological observations.