QCD Sum Rules for Exclusive Decays of Heavy Mesons

Applications of QCD sum rules to exclusive decays of heavy mesons are reviewed. In detail, we discuss the calculations of the B and $D$ decay constants, the heavy-to-light form factors $f^+(p^2)$ and $f^0(p^2)$, and the strong couplings $g_{B^*B\pi}$ and $g_{D^*D\pi}$. Predictions are presented for the semileptonic weak decays $B \to \pi \bar{l} \nu_l$ and $B \to \rho \bar{l} \nu_l$, and used to extract $V_{ub}$ from the measured decay widths. Results are also shown on $D \to \pi \bar{l} \nu_l$ and $D^* \to D \pi$. Furthermore, we reconsider the factorization hypothesis in nonleptonic two-body decays, and describe a sum rule estimate of the nonfactorizable contribution to the amplitude of $B \to J/\psi K$.