Forget WIMPs, Axions And MACHOs: Could WIMPzillas Solve The Dark Matter Problem?

There's perhaps no more fundamental question to ask than, "what is the Universe made of?" What we see, directly, is dominated by normal matter: things made of particles we know well like protons, neutrons, and electrons, and the photons they emit. But our measurements of the largest structures in the Universe indicate that this is only 5% of what's out there. The rest is dark matter and dark energy. While dark energy might be an inherent property of space itself, we assume, because of its gravitational effects, that dark matter clusters, clumps, and is made of particles.

But what, exactly, is dark matter? And, moreover, can we be certain it exists? Thereare a huge suite of detectors and experiments out there searching for it, and yet no robust, verified, direct detection has ever been reported. There is no smoking gun we can point to and say, "this was an event caused by an interaction with dark matter." The overwhelming majority of detectors out there are looking for WIMP-type dark matter, with a small contingent also looking for axions. (MACHOs, or other sources of "normal" dark matter, have been ruled out.) But all of this may be misguided. Dark matter might not be any of those things we're looking for. In fact, it's arguable that the candidate with the best motivations for it have no experiments to their name at all: WIMPzillas!