Semileptonic B_(q)to D^(ast)_(q)lν (q=s, d, u) transitions in QCD

The form factors relevant to $B_{q}\to D^{\ast}_{q}(J^{P}=1^{-})\ell\nu$ $(q=s, d, u)$ decays are calculated in the framework of the three point QCD sum rules approach. The heavy quark effective theory prediction of the form factors are obtained. The total decay width and branching ratio for these decays are also evaluated using the $q^2$ dependencies of these form factors.