Axions

Hypothetical, extremely light, neutral particles originally proposed to resolve the Strong CP Problem in quantum chromodynamics (QCD) - the puzzling question of why the strong nuclear force treats matter and antimatter symmetrically. Beyond this original motivation, axions have become a leading candidate for cold dark matter. They are predicted to be produced copiously in the early universe, forming a coherent, wave-like field that permeates the cosmos. Being exceptionally light and weakly interacting, they would behave as a "fuzzy" or "wave-like" form of dark matter, potentially influencing the formation of small-scale structures in a unique way. Their discovery would simultaneously solve a fundamental particle physics puzzle and reveal the identity of the universe's dominant matter component.