Scalar glueballs in QCD appear as a result of violation of global conformal (scale) symmetry - the energy-momentum tensor has a nonzero trace. According to the Goldstone theorem, this (violation of global symmetry) corresponds to the appearance of scalar massless bosons.(adsbygoogle = window.adsbygoogle || []).push({});

Why, then, are the scalar glueballs massive, and the massless variant is not considered anywhere?

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# A Why is a glueball not massless, if it's a Goldstone boson?

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