axion

1. (physics) A hypothetical subatomic particle postulated to resolve certain symmetry problems concerning the strong nuclear force.Examples: "2000 Summer/Fall, John Clarke, Superconductivity: A Macroscopic Quantum Phenomenon, Rene Donaldson, Bill Kirk (editors), Beam Line, Volume 30, Number 2, Stanford Linear Accelerator Center, page 47, The axion is a candidate particle for the cold dark matter that constitutes a large fraction of the mass of the Universe."; "In summary, the first version of gravity-mediated supersymmetry breaking has the advantage of giving an axion mass that is within cosmological bounds, while the second version has the advantage of giving the gauginos masses that are comparable to the masses of the squarks and sleptons."; "Let us begin with a disclaimer: axions, a, have been conjectured to exist on theoretical grounds, but have not as yet been observed. They are supposed to be very light particles that interact very weakly with matter."