Can dark matter ever be extra-dimensional?
Actually, yes, there are some theories in which dark matter involves extra dimensions. One plausible candidate is a “Kaluza-Klein” particle, which is an extra-dimensional excitation; it may have some observable annihilation signatures. There are other ideas involving extra dimensions, too. Experiments at high energy particle colliders in the next decade or so will test the various theories that predict WIMP and extra-dimensional dark matter.
