$\eta_{b}BB^{\ast}$ vertex from QCD sum rules
  The form factor and the coupling constant in the $\eta_{b}BB^{\ast}$ vertex are evaluated in the framework of three-point QCD sum rules. The correlation functions responsible for the vertex is evaluated considering contributions of both $B$ and $B^{\ast}$ mesons as off-shell states. The form factors obtained are different for the two cases, whereas the final results of the coupling constant are compatible. 
Chun-Yu Cui, Yong-Lu Liu and Ming-Qiu Huang
hep-ph