Answer: axion

AnswerCrossword Clue
AXIONHypothetical particle
AXIONPhysicist's proposed particle
AXIONHypothetical physics particle
AXIONHypothetical fundamental particle
AXIONHypothetical particle in cold dark matter
AXIONParticle theorized in 1977
axionhypothetical particle having no charge, zero spin, and small mass: postulated in some forms of quantum chromodynamics
axiona hypothetical subatomic particle of low mass and energy that is postulated to exist because of certain properties of the strong force