  We extract the K+K- couplings of the isoscalar scalar mesons sigma/f_0(600)
and f_0(980) from pi pi to pi pi / K K scatterings and found: |g_{sigma K+K-}|/
|g_{sigma pi+pi-}|= 0.8 and |g_{f_0 K+K-}|/ |g_{f_0 pi+pi-}|= 1.7. These
results, together with the tiny "direct" gamma gamma width of the sigma and its
large hadronic width, are a strong indication for the gluonium/glueball nature
of the sigma-meson, as predicted by QCD spectral sum rules (QSSR) + some
low-energy theorems (LET), while some other assignements (pi pi molecule,
tetraquark state and ordinary qq meson) do not satisfy simultaneously these
requirements from the data. These properties suggest that the sigma can be a
scalar meson associated to the U(1)V conformal anomaly like is the eta'-meson
for the U(1)A anomaly.
