Masses, decays and mixings of gluonia in QCD

We compute the masses and decay widths of the gluonia using QCD spectral sum rules and low-energy theorems. In the scalar sector, one finds a gluonium having a mass M-G = (1.5 +/- 0.2) GeV, which decays mainly into the U(1)(A) channels eta eta' and 4 pi(0). However, for a consistency of the whole approach, one needs broad low-mass gluonia (the sigma(B) and its radial excitation), which couple strongly to the quark degrees of freedom similarly to the eta' of the U(1)(A) sector. Combining these results with the ones for the (q) over bar q quarkonia, we present maximal gluonium-quarkonium mixing schemes, which can provide quite a good description of the complex spectra and various decay widths of the observed scalar mesons sigma(1), f(o)(0.98), f(o)(1.37), f(o)(1.5) and f(J)(1.71). In the tensor sector, the gluonium mass is found to be M-T similar or equal to (2.0 +/- 0.1) GeV, which makes the zeta(2.2) a good 2(++) gluonium candidate, even though we expect a rich population of 2(++) gluonia in this region. In the pseudoscalar channel, the gluonium mass is found to be M-P similar or equal to (2.05 +/- 0.19) GeV, while we also show that the E/iota(1.44) couples more weakly to the gluonic current than the eta'(0.96), which can favour its interpretation as the first radial excitation of the eta'(0.96). (C) 1998 Published by Elsevier Science B.V.