$B^{\ast}_{s1}B^{\ast}K$ form factor from QCD sum rules
  In this article, we calculate the form factors and the coupling constant of the $g_{B^{\ast}_{s1}B^{\ast} K}$ vertex in the framework of the three-point QCD sum rules. Three point correlation functions responsible for the vertex are evaluated by considering both $B^{\ast}$ and $K$ mesons as off-shell states. The form factors obtained are different if the $B^{\ast}$ or the $K$ meson is off-shell but give the same coupling constant. 
Chun-Yu Cui, Yong-Lu Liu and Ming-Qiu Huang
hep-ph