An axion is a elementary particle theorized in 1977 by the Peccei–Quinn theory. It was used to solve the strong CP problem in quantum chromodynamics (QCD). If these axions do exist in a specific mass range, they could be a possible part of cold dark matter. There is also evidence of solar axions (axions from the Sun). Also if these axions exist there is evidence that they can go faster than the speed of light.