The case for co-decaying dark matter
http://phys.org/news/2016-12-case-co-decaying-dark.html
There isn't as much dark matter around today as there used to be. According to one of the most popular models of dark matter, the universe
contained much more dark matter early on when the temperature was hotter. As the universe cooled, the dark matter annihilated away, at least
up until a point when thermal equilibrium was reached and the annihilations ceased, resulting in the number of dark matter particles in
the universe "freezing out" and remaining roughly constant.
Although this scenario, called "the weakly-interacting-massive-particle" (WIMP) scenario,
has been researched extensively, it's still unclear if the dark matter is indeed a WIMP.
In a new study published in Physical Review Letters, Cornell physicists Jeff Asaf Dror, Eric Kuflik, and Wee Hao Ng have proposed a new mechanism
for dark matter freeze-out in which there is not one but many dark sector particles that all co-decay to produce the observed dark matter density.
One or more of these particles are potential candidates for dark matter.
"For a long time, the Weakly Interacting Massive Particle (WIMP) has been the paradigm for explaining the particle nature of dark matter," Kuflik
told Phys.org. "Most experiments to discover dark matter were designed to find something that looks like a WIMP. The motivation for our work was to
try to find other explanations for the nature of dark matter that would be experimentally searched for in a qualitatively different way than the WIMP.