Axion
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An axion is a hypothetical elementary particle originally postulated by the Peccei–Quinn theory in 1977 to resolve the strong CP problem in quantum chromodynamics. If axions exist and have low mass within a specific range, they are of interest as... Wikipedia
Interactions: Gravitational, electromagnetic, strong nuclear, weak nuclear
Mass: 10−5 to 1 eV/c2
Spin: 0
Status: Hypothetical
Symbol: A0, a, θ