"I'm on it already."
One of the earliest Dark Matter theories was that of MACHOs.
MACHOs--Massive Compact Halo Objects; theorized massive compact objects the size of small stars formed of dark matter and present in the outer reaches (halos) of galaxies. May be formed of Mirror Matter. This theory most likely still does not provide sufficient "dark matter" to explain observed gravimetric phenomena.
But wait, you say, what's this about Mirror Matter? Is that the universe with the evil Kirk in it?
Well, maybe but not quite. To go much further, we'll have to run through some related, supporting theories and definitions.
Negativity--When Dirac discovered electron spin, a problem arose in the equations. Since the equation employed a square root, it allowed for a solution both positive and negative. (The square root is present because Einstein's relativity equation uses the speed of light squared.) That is, mathematically, electrons could possess negative energy. This led him to propose antimatter (matter possessed of negative energy) and the further theory of antiparticles in general. The antielectron or positive electron (positron) is supposed to be observed in the form of cosmic rays.
This lead to the idea of Mirror Matter via the Symmetry argument.
Mirror Matter--Every type of particle in nature has a mirror partner that is utterly invisible (does not interact with light) and can be detected only by its gravity.
SUSY--Supersymmetry. A mathematical framework now accepted as proven that proposes, as a function of the principle of conservation of energy, the net state of the universe must be zero-sum and have particular, physical symmetry. Actual experimental evidence of SUSY is effectively non-existent despite the common assumption of its infallibility. The primary argument in its favor is the philosophical principle that math arises from the forms of nature. Rather than simply a human invention for book-keeping, math is an intrinsic part of the natural form observed and recorded by humans.
Which in turn gives us the nomenclatural nightmare of Sparticles.
Sparticles--Supersymmetric partner particles. The theory that there exists a new subatomic partner for every kind of particle now known within the quantum dimensions (sizeless dimesnions). SUSY quantum theory adds the idea of a fermionic dimension as well as the traditional, observable bosonic dinension. Fermionic (fundamental matter particles) and bosonic (fundamental force particles) particles are necessary to support SUSY via the argument that force and matter are to aspects of the same thing (again, a legacy of Einstein). This argument has merit, beyond merely E=mc2, since the defining feature of a boson vs. a fermion is simply spin. Sparticles are named by placing an 's' in front of the particle they theoretically partner with. I. E. quarks and squarks. Force Sparticles gain 'ino' at the end. I. E. photons and photinos.
Next Time: WIMPs, SIMPs, and Q-Balls!