Physicist suggests new experiments could make or break axion as dark matter theory: (Phys.org)—Leslie Rosenberg, a physicist with the University of Washington has published a paper in Proceedings of the National Academy of Sciences, describing the current state of research that involves investigating the possibility that axions are what make up dark matter. He also offers some perspective on the work suggesting that at least one project is likely to lead to either proving or disproving that axions are dark matter. For several years now, scientists have been hard at work trying to detect WIMPs, the thinking has been that if they can be detected, than it would go a long way towards proving that they are what makes up dark matter—the theoretical stuff that is now believed to make up approximately 85 percent of all mass in the universe. Unfortunately, despite their best efforts, scientists have not yet been able to detect the presence of a single one, causing some to wonder if they exist at all. That doubt has led some scientists to consider other types of particles as dark matter candidates—one of them is the neutrino, though more and more it appears to be falling from favor. Another is the axion, a particle first theorized in the early 70's. One of its major proponents is Rosenburg, who has been developing experimental devices with the purpose of either proving that dark matter is made up of axions, or it is not. Read more at: http://phys.org/news/2015-01-physicist-axion-dark-theory.html#jCp
Axions has been a dark matter candidate for a while. Until someone comes up with an experimental result, all guesses remain open.
I like Rosenburg's skeptical / experimental approach. But it's hard to see how two massless photons can interact in a way to produce a particle with enough mass to account for dark matter. The math is certainly involved to make such a prediction, but much longer odds often pay off in theoretical physics.
