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 vflat. The dark matter velocity anisotropy parameter is therefore betaDM → -infinity (purely tangential), in sharp contrast to the Standard Halo Model (betaSHM = 0, isotropic). In the solar frame, the effective DM wind speed is sigmaₑff = fcold * vflat / 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 sigmaₗos/vflat = 0. 600 exactly using standard N-body simulation parameters.