Abstract

Glueballs, i.e. bound states of gluons, were predicted since the early days of Quantum Chromodynamics. They are expected to exist because gluons interact strongly with themselves (`gluons shine in their own light’). Indeed, within Lattice QCD a full spectrum of glueballs has been obtained. The lightest glueball is predicted to be a scalar state and has a mass about 1.7 GeV: as a consequence,intensive research concentrated on the resonances f0(1500) and f0(1710) as possible glueball candidates. However, for other quantum numbers, the situation is much less clear: future experimental results and theoretical work are needed in order to identify candidates and in order to study their decay properties. In this talk, we review the theoretical status of glueballs’ research: different models are compared, both for what concerns the scalar glueball and the other quantum numbers. The role of mixing of glueballs with ordinary quark-antiquark states is addressed. Perspectives for future research on this important subject of hadronic physics are described.