Asymptotically flat galactic rotation curves in gravity theory

We present a new set of four-geometries exhibiting asymptotically flat galactic rotation curves. These are found as explicit solutions to 5D vacuum Hilbert-Palatini theory, where the fifth dimen sion has vanishing proper length. In the emergent 4D dynamics, governed by the condition that the Ricci scalar must vanish (upto a cosmological constant), these correspond to anisotropic effective pressure. The enhancement in the deflection angle of a light ray penetrating the halo is obtained, which could provide a realistic testing ground for the model as a purely geometric alternative to `dark matter'. For very large halo radii, the leading nonbaryonic contribution to the bending angle is predicted to be 3π v²/2c² (v being the asymptotic rotational velocity), a constant that is different from the result for an isothermal CDM halo.