Probing thess content of the η and η ′ mesons and considering mixing between these states as well as gluonic contributions, the form factors responsible for semileptonic D s → (η, η ′ )lν transitions are calculated via light cone QCD sum rules. Corresponding branching fractions and their ratio for different mixing angles are also obtained. Our results are in a good consistency with experimental data as well as predictions of other nonperturbative approaches.

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Using the factorization approach and considering the contributions of the currentcurrent, QCD penguin and electroweak penguin operators at the leading approximation, the decay amplitudes and decay widths of B q → D q (D * q )P and B q → D q (D * q )V transitions, where q = u, d, s and P and V are pseudoscalar and vector mesons, are calculated in terms of the transition form factors of the B q → D q and B q → D * q . Having computed those form factors in three-point QCD sum rules, the branching fraction for these decays are also evaluated. A comparison of our results with the predictions of the perturbative QCD as well as the existing experimental data is presented. *

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