SU(3) corrections to B → Dl overlineν form factors at O( {1}/{M})

We compute the O( {1}/{M}, m _s) heavy quark and SU(3) corrections to overlineB_s → D _seν form factors. In the limit of vanishing light quark mass, overlineB_s → D _seν form factors are given in terms of the the overlineB → Deν form factors, the leading order chiral parameter g, and two O( {1}/{M}) chiral parameters g₁ and g₂. All the chiral parameters can be extracted, in principle, from other heavy meson decays. Analytic counterterms proportional to the strange quark mass are presented for completeness, but no predictive power remains when they are included. Anomalously large loop corrections warn of poor convergence of the heavy quark chiral symmetry expansion for these processes. This suggests that naive extrapolations of overlineB → D form factors relying on heavy quark and chiral symmetries, as often used in monte carlo simulations of lattice QCD, may incur large errors.