A particle proposed 50 years ago may be masquerading as a fraction of a neutrino. If so, it could help to explain the origins of dark matter, the mysterious, invisible stuff that makes up more than 80 per cent of the universe's matter.
Proposed in the 1960s, the Goldstone boson is supposed to be part of the Higgs mechanism, which gives mass to some other fundamental particles. But no hints of it have been seen in nature so far.
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