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 $g_{B^{\ast }B\pi }$ and $g_{D^{\ast }D\pi }$. Predictions are presented for the semileptonic weak decays $B\to \pi \bar{l}{\nu }_l$ and $B \to \rho \bar{l} \nu_l$,andusedtoextract$V_{ub}$ from the measured decay widths. Results are also shown on $D\to \pi \bar{l}{\nu }_l$ and $D^{\ast }\to D\pi$. 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 $B\to J\mathrm{/}\psi K$.