also with the inclusion of short–distance QCD corrections. Their numerical result for the ratio of form factors is between 1.09 and 1.18. The parameters that cause the largest uncertainty in the ratio are $m_{c}$ and $\mu $. Again, the rates vanish at $y=1$ due to phase space. To determine the LHS of (\[eqDV6\]) experimentally one should access the region nearby and extrapolate to the point of $y=1$.

Ligeti and Wise give a model-independent method [@LW] which is based on the study [@bg] of the double ratio of form factors $(f^{(B\rightarrow\rho      )}/     f^{(B\rightarrow
K^{*})})/(f^{(D\rightarrow\rho   )}/f^{(D\rightarrow   K^{*})})$. They claim that this double ratio is equal to unity in the $SU(3)$ limit, and in the limit of heavy quark symmetry so that a determination of $|V_{ub}|$ is possible using information obtainable from the decay modes $B\rightarrow   \rho  \ell
\bar{\nu}_{\ell}$, $B\rightarrow    K^{*}   \nu    \bar{\nu}$, $D\rightarrow  \rho  \bar{\ell }  \nu_{\ell}$ and $D\rightarrow
K^{*} \bar{\ell}  \nu_{\ell}$. They use a pole model to get away from the zero–recoil point. Since the maximum values for $y$ are different for $B$ and $D$ decays, $y_{max}=3.5$ and $y_{max}=1.3$, respectively, they limit $y$ for the $B$ decays to lie in the range $1< y  <1.5$. Provided $f^{(D\rightarrow\rho
)}(y)/f^{(D\rightarrow  K^{*})}(y)$ is almost 