Decay constant of eta-meson f is calculated on the basis of the QCD sum rule method. An instanton contribution is taken into account. The result is f = 0.17 GeV.
Decay Constants of $D_{sJ}^*$(2317) and $D_{sJ}$(2460)
Mass and decay constant of the newly observed exotic $X(5568)$ state
Application of Bayesian statistics to the sector of decay constants in three-flavour ChPT
