From ? and ? to glueballs?

Abstract We discuss the effect of η-ή mixing and of axial current anomalies on various decay processes. We describe the 2γ decays of η and ή the radiative decays of low-lying vector mesons as well as the decays η → 3π, J/ψ → ηγ and J/ψ → ήγ and discuss briefly the enhancement of ή in Ds decays, suggesting an explanation in terms of gluon-mediated processes. The importance of the decays of the glueballs into ηή channels is stressed, in particular in connection with the candidates f o(1500) and f o(1590).