I mentioned in an earlier post that Stephano Profumo gave an excellent departmental colloquium here at USC on the subject of Dark Matter, addressing the questions of what it is, what some of the promising models and theories of particle physics have to say about it, and the prospects for (relativity) near future experiments and observations.
The matter content of the Universe appears to be dominated by a form of matter whose existence is inferred on the basis of its gravitational effects, and whose fundamental microscopic nature is at present unknown. This form of matter must be qualitatively different from the ordinary matter (neutrons, protons, electrons) that accounts for planets, stars and galaxies, and must couple very weakly to the known particles of the Standard Model. In this colloquium, I will review and outline the wide ensemble of evidence for dark matter, the best motivated dark matter candidates, and the ongoing experimental and theoretical effort in the quest for the identification of this elusive, and yet fundamental, constituent of the Universe.
His penultimate slide (shown above) was really an excellent summary of the two key approaches to learning more about out universe’s complement of Dark Matter. [Update: That slide is actually due to Sean Carroll. See this comment, and this link.]
Here’s a slide with what he meant in more traditional scientific terms: