Dark matter self-interactions from higher dimensional gravity

It has recently been suggested that, in a brane-world scenario with large extra dimensions, short-distance gravitational interactions can enhance the dark matter scattering cross section in a velocity-dependent way. Such a modification may then help to address possible problems with noninteracting cold dark matter on galactic and subgalactic scales. We argue that, considering the singular character of the higher-dimensional Newtonian potential, the scattering cross section is UV dependent, depending ultimately on the underlying quantum gravity theory considered. We demonstrate that, for a wide class of unitary short-distance regularizations, the actual cross section is velocity independent and does not significantly affect the dark matter substructure. We comment on the problem of thermalization of ultralight cold dark matter by gravitational interactions in the early universe.