Scale-Dependent Dimensionality with Local Screening and Emergent Phenomena

We propose a single dynamic parameter γ(x, t) that controls the effective dimensionality of spacetime in a scale- and density-dependent manner. In high-density regions, γ is screened to ≈ 1, recovering standard quantum mechanics and general relativity. In extremely lowdensity environments, γ approaches ≈ 1.10, yielding deff ≈ 4.1, weakened effective gravity, and emergent dark energy. The framework is realized via a density-dependent measure v(ρel) in the action, leading to modified Friedmann equations and variable-order fractional quantum mechanics. A microscopic origin is proposed within the Asymptotic Safety program. The model is consistent with current precision constraints and makes clear falsifiable predictions for upcoming experiments.