Spectral Functions for Heavy-Light Currents and Form Factor Relations in   Hqet
  We derive relations among form factors describing the current-induced transitions: (vacuum) $\rightarrow B,B^{*}, B \pi, B^{*} \pi, B \rho$ and $B^{*} \rho$ using heavy quark symmetry. The results are compared to corresponding form factor relations following from identities between scalar and axial vector, and pseudoscalar and vector spectral functions in the heavy quark limit. 
C.A.Dominguez, J.G.Korner and K.Schilcher