Abstract
We compute the masses and decay widths of 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
η
η
′
and 4
π
0
. However, for a consistency of the whole approach, one needs broad-low mass gluonia (the
σ
and its radial excitation), which couple strongly to the quark degrees of freedom similarly to the
η
′
of the
U(1
)
A
sector. Combining these results with the ones for the
q
¯
q
quarkonia, we present maximal quark-gluonium mixing schemes, which can provide quite a good description of the complex spectra and various decay widths of the observed scalar mesons
σ(1.0),
f
0
(0.98),
f
0
(1.37),
f
0
(1.5)
and
f
J
(1.71)
. In the tensor sector, the gluonium mass is found to be
M
T
≃(2.05±0.19)
GeV, which makes the
ζ(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
≃(2.05±0.19)
GeV, while we also show that the
E/ι(1.44)
couples more weakly to the gluonic current than the
η
′
, which can favour its interpretation as the first radial excitation of the
η
′
(0.96)
.