Axions are so hot right now.
Dark Matter purportedly binds galaxies together, and comprises the bulk of the mass in our universe. Dark Matter is called “dark” because it doesn’t appear to interact with electromagnetic fields: it doesn’t glow or reflect light. Astronomers and Physicists assert its existence without direct evidence for such particles for a number of reasons. First, the amount of matter required by the apparent dynamics of the universe is far more than we can see. Second, applications of general relativity to the distortions of starlight associated with galaxy collisions and mergers provide compelling evidence for its presence.
These are technical issues far removed from our daily experience. This makes dark matter a hard thing to explain, although here's a pretty good attempt!
The failure to observe so-called WIMP particles (think, really heavy neutrinos) either directly through experiments deep underground or indirectly via Supersymmetry searches at the LHC was something of a surprise to many particle physicists. The so-called WIMP miracle explanation for the apparently unstable mass of the Higgs Boson was culturally baked in amongst high energy theorists. In retrospect WIMPs weren't so fated.
Without recourse to WIMPs, the next best candidate for dark matter appears to be axions. Axions are abundant in models descending from String Theory, and can be present almost whenever there are nuclear forces. They were originally proposed to solve another sort of technical problem in the strong nuclear force.
Last summer there was a bit of early hope that axions associated to the sun might have been observed. Although, like many initial findings, those conclusions didn’t stand up to further scrutiny.
Incidentally, Helen Quinn - the Quinn behind the famous Pecci-Quinn symmetry - originally proposed the axion as a solution that technical problem. Quinn has found a second career in retirement, pushing to overhaul science education.
