Obtaining the strong coupling constants g_{J/\psi D_s D_s} and g_{\phi   D_s D_s} from QCD Sum Rules
  The form factors and coupling constants of the meson vertices J/\psi D_s D_s and \phi D_s D_s were calculated using three point correlation functions within the QCD Sum Rules formalism. We have considered the cases where \phi, D_s and J/\psi mesons are off-shell obtaining, for each vertex, two different form factors and its corresponding coupling constants, namely g_{J/\psi D_s D_s} = 6.20^{+0.97}_{-1.15} and g_{\phi D_s D_s} = 1.85^{+0.22}_{-0.23}. 
M. E. Bracco, M. Chiapparini and B. Os\'orio Rodrigues
hep-ph