Constituent gluon interpretation of glueballs and gluelumps

Arguments are given that support the interpretation of the lattice QCD glueball and gluelump spectra in terms of bound states of massless constituent gluons with helicity 1. In this scheme, we show that the mass hierarchy of the currently known gluelumps and glueballs is mainly due to the number of constituent gluons and can be understood within a simple flux tube model. It is also argued that the lattice QCD 0^+- glueball should be seen as a four-gluon bound state. We finally predict the mass of the 0^- state, not yet computed in lattice QCD.