Chiral corrections to the scalar form factor in Bq→Dq transitions

We consider chiral loop corrections to the scalar form factor in Bq→Dqlν decays. First we consider chiral corrections to the 1/mQ suppressed operators and then we propose a procedure for the extraction of the relevant form factor using lattice QCD results. In particular, the extraction of a B*→D* matrix element on the lattice can be used to determine all the necessary 1/mQ suppressed contributions to the scalar form factor in B→D transitions. In the case of (Bs→Ds)/(B→D) decay rate ratios we speculate that effects of kinematics and chiral corrections tend to cancel for the scalar form factor contributions. In particular the 1/mQ suppression of chiral corrections is compensated by the potentially large SU(3) flavor symmetry breaking corrections. The calculated corrections are relevant for the precise determination of possible new physics effects in Bq→Dqlν decays.