Purely Tangential Dark Matter Orbits in the U-Cell Model: Velocity Anisotropy and Signatures in Direct Detection

The U-Cell Model (UCM) predicts that dark matter occupies only tangential substrate modes in virialized halos. Radial modes are dynamically unstable — swept inward by the gravitational background flow and absorbed by the central mass concentration (Sgr A*). Tangential modes form stable circular orbits at group velocity v_flat. The dark matter velocity anisotropy parameter is therefore beta_DM → -infinity (purely tangential), in sharp contrast to the Standard Halo Model (beta_SHM = 0, isotropic). In the solar frame, the effective DM wind speed is sigma_eff = f_cold * v_flat / sqrt(2) ≈ 108 km/s (Milky Way), not the bulk circular speed of 233 km/s assumed by the SHM. Three falsifiable predictions follow: (1) directional detectors see recoils exclusively from the tangential direction; (2) the annual modulation amplitude is ~3.7x larger than the SHM prediction; (3) the recoil spectrum shifts to lower energies. The apparent 30% discrepancy with Prada et al. (2003) satellite kinematics is resolved by correctly applying the Jeans equation to the baryonic tracer population in the UCM isothermal potential, yielding sigma_los/v_flat = 0.600 exactly using standard N-body simulation parameters.