Semileptonic Form-factors from B-> K* gamma Decays in the Large Energy Limit

Abstract

Making use of the measurement of the $B\to K^{\ast }\gamma$ branching ratio together with the relations following from the limit of high recoil energy, we obtain stringent constraints on the values of the form-factors entering in heavy-to-light $B\to V\ell {\ell }^{\prime }$ processes such as $B\to K^{\ast }{\ell }^{+}{\ell }^{-}$, $B\to K^{\ast }\nu \bar{\nu }$ and $B\to \rho \ell \nu$ decays. We show that the symmetry predictions, when combined with the experimental information on radiative decays, specify a severely restricted set of values for the vector and axial-vector form-factors evaluated at zero momentum transfer, $q^2=0$. These constraints can be used to test model calculations and to improve our understanding of the $q^2$-dependence of semileptonic form-factors. We stress that the constraints remain stringent even when corrections are taken into account.

Comments: 10 pages, 1 ps figure