$D^*D\pi$ and $B^*B\pi$ form factors from QCD Sum Rules
  The $H^*H\pi$ form factor for H = B and D mesons is evaluated in a QCD sum rule calculation. We study the Borel sum rule for the three point function of two pseudoscalar and one vector meson currents up to order four in the operator product expansion. The double Borel transform is performed with respect to the heavy meson momenta. We discuss the momentum dependence of the form factors and two different approaches to extract the $H^*H\pi$ coupling constant. 
F.S. Navarra, M. Nielsen, M.E. Bracco, M. Chiapparini and C. L. Schat