Physical first-principles derivation of the pseudo-isothermal halo profile ρ (r) = ρ₀/ (1+ (r/rc) ²) within the U-Cell Model (UCM). The universal cold parameter fcold = √ (2−π/2) ≈ 0. 6551 is derived analytically from the substrate dispersion relation without free parameters. Tested against 150 SPARC galaxies (Li et al. 2020): median χ² = 0. 73, 71% of fits with χ² < 2. The systematic deterioration at high masses is physically interpreted as the onset of baryonic feedback beyond the current UCM formulation.
Norbert Prebeck (Fri,) studied this question.