"Shut up, cat, I got it."
Back to the theories:
WIMPs--Weakly Interacting Massive Particles. Mathematically, Sparticales must be significantly much more massive than their partners and interact only where very weak nuclear forces are involved. Thus, SUSY particles are often discussed as WIMP. Theoretically, WIMPs would have been formed during the big bang but, being unstable, decayed into lighter particles. This makes the most likely candidate for actual detection the LSP (lightest supersymmetrical particle) considered to be either the photino or something referred to as the neutralino (because it may be a quantum mixture of different neutral sparticles). It has been postulated that MACHOs may be comprised of WIMPs or that WIMPs permeate the universe to account for the matter discrepancy.
Neutrinos--A neutral charge particle of mass similar to that of an electron. Neutrinos have been tentatively detected through experiments within nuclear reactors. Neutrinos may make up a portion of Dark Matter but lack sufficient mass to account for the whole. Further, many astronomers now argue (based on cosmic background radiation) that Dark Matter cannot be baryonic matter. Neutrinos are actually fermionic but act similar enough to baryonic to remove them from contention as an explanation. Because of their properties, neutrinos would form hot Dark Matter and most astronomers (again based on the background radiation) believe Dark Matter must be cold. (Hot and cold referring to mass, interaction, etc.)
SIDM (also called SIMPs)--Self-Interacting Dark Matter (Strongly Interacting Massive Particles). Big fat WIMPs that react strongly instead of weakly, considered to be self-interacting because they have never been observed and therefore cannot be interacting with non-dark matter.
Q-Balls--Lumps of matter that may have formed when sparticles coagulated during the hot dense phase of the early big bang universe. The real fun of Q-Balls is not their possibility of explaining Dark Matter (very unlikely) but that they would blow up REAL good. These would be coagulated balls of squarks and sleptons that, rather than being the actual explosive themselves, would be a quantum catalyst. Fed by a proton stream, the internal sparticles of a Q-Ball would rip proton quarks apart, releasing the fundamental energy of the quarks (about 100X H-bomb yield).
Q-Balls are a good example of where the sci-fi writer in me takes a walk away from the critical scientist. As a theory, even the guys who came up with the idea of Q-Balls say it's highly unlikely and fairly weak. But as an idea to use in a story, it's rich with possibilities and it's scientifically plausible.
Next Time: Quintessence