IV.R129 — Glueballs and the mass gap

Glueball existence is a direct consequence of the mass gap: without a gap there would be massless gluonic excitations, but confinement ensures every excitation above vacuum carries positive mass; the lightest glueball at ~1.5 GeV satisfies m_gb ~ 2pi/sigma_tau^(1/2), though experimental identification is complicated by mixing with nearby scalar mesons.