Gravitational-recoil effects on fermion propagation in space-time foam

Motivated by the possible experimental opportunities to test quantum gravit y via its effects on high-energy neutrinos propagating through space-time f oam, we discuss how to incorporate spin structures in our D-brane descripti on of gravitational recoil effects in vacuo. We also point to an interestin g analogous condensed-matter system. We use a suitable supersymmetrization of the Born-Infeld action for excited D-brane gravitational backgrounds to argue that energetic fermions may travel slower than the low-energy velocit y of light: delta c/c similar to -E/M. It has been suggested that Gamma-Ray Bursters may emit pulses of neutrinos at energies approaching 10(19) eV: t hese would be observable only if M greater than or similar to 10(27) GeV.