Weak Decays in the light--front Quark Model

Abstract

We study the form factors of heavy--to--heavy and heavy--to--light weak decays using the light--front relativistic quark model. For the heavy--to--heavy $B\text{ra}{D}^{(\ast )}$ semileptonic decays we calculate the corresponding Isgur--Wise function for the whole kinematic region. For the heavy--to--light $B\text{ra}P$ and $B\text{ra}V$ semileptonic decays we calculate the form factors at $q^2=0$; in particular, we have derived the dependence of the form factors on the $b$--quark mass in the $m_b\text{ra}\infty$ limit. This dependence can not be produced by extrapolating the scaling behavior of the form factors at $q_{max}^2$ using the single--pole assumption. This shows that the $q^2$ dependence of the form factors in regions far away from the zero--recoil could be much more complicated than that predicted by the single--pole assumption.

Comments: 24 pages, Latex, Postscript figure included at the end