Emergent Solution to the Strong CP Problem.

We construct a theory in which the solution to the strong CP problem is an emergent property of the background of the dark matter in the Universe. The role of the axion degree of freedom is played by multibody collective excitations similar to spin waves in the medium of the dark matter of the Galactic halo. The dark matter is a vector particle whose low energy interactions with the standard model take the form of its spin density coupled to GG[over ˜], which induces a potential on the average spin density inducing it to compensate θ[over ¯], effectively removing CP violation in the strong sector in regions of the Universe with sufficient dark matter density.

Superweakly interacting massive particle solutions to small scale structure problems.

Collisionless, cold dark matter in the form of weakly interacting massive particles (WIMPs) is well motivated in particle physics, naturally yields the observed relic density, and successfully explains structure formation on large scales. On small scales, however, it predicts too much power, leading to cuspy halos, dense cores, and large numbers of subhalos, in apparent conflict with observations. We consider super-WIMP dark matter, produced with large velocity in late decays at times 10(5) - 10(8) s.

Superweakly interacting massive particles.

We investigate a new class of dark matter: superweakly interacting massive particles (super-WIMPs). As with conventional WIMPs, super-WIMPs appear in well motivated particle theories with naturally the correct relic density. In contrast to WIMPs, however, super-WIMPs are impossible to detect in all conventional dark matter searches.