Comment on $V_{ub}$ from Exclusive Semileptonic B and D Decays

Abstract

The prospects for determining $|V_{ub}|$ from exclusive B semileptonic decay are discussed. The double ratio of form factors $(f^{B\to \rho }/f^{B\to K^{\ast }})/(f^{D\to \rho }/f^{D\to K^{\ast }})$ is calculated using chiral perturbation theory. Its deviation from unity due to contributions that are non-analytic in the symmetry breaking parameters is very small. Combining experimental data obtainable from (B->rho l nu), (B->K* l l) and (D->rho l nu) can lead to a model independent determination of $|V_{ub}|$ with an uncertainty from theory of about 10%.

Comments: 14 pages, 3 figs, minor typos corrected, to appear in Phys. Lett. B