A study of the gηcDD coupling constant from the QCD sum rules

In this work, we calculate the form factor and the coupling constant of the charmed vertex ηcD*D using the QCD sum rules (QCDSR) for the case where the D* meson is considered off-shell. This is accomplished by using not only the perturbative contribution of the OPE series but also the non-perturbative effects of the gluon condensates. The form factor of this vertex presents two tensor structures, both of which were analysed. The coupling constant is obtained by the extrapolation of the exponentially parametrized form factor curve to the pole of the D* meson.