Dark matter
In Lambda-CDM, dark matter is an extremely inert form of matter that does not interact with both ordinary matter (baryons) and light, but still exerts gravitational effects. To produce the large-scale structure we see today, dark matter is "cold" (the 'C' in Lambda-CDM), i.e. non-relativistic. Dark matter has not been conclusively identified, and its exact nature is the subject of intense study. The leading dark matter candidates are weakly interacting massive particles (WIMPs) and axions. Both of these are new elementary particles not included in the Standard Model of Particle Physics. A major difference between the two is their mass: WIMPs generally have masses in the GeV range, while axions are much lighter, with masses in the meV range or lower.