THE QCD SUM-RULE APPROACH FOR THE SEMILEPTONIC DECAY OF THE D-MESON OR B-MESON INTO A LIGHT MESON AND LEPTONS

We use the method of QCD sum rules to treat the semileptonic weak deca y of the D or B meson into a light meson and leptons. To obtain the tr ansition form factors, we adopt the two-point Green's function in the presence of an external vector or axial-vector field. We find that thi s method can be related approximately to the traditional three-point G reen's function in the heavy quark limit (m(Q) --> infinity). Unlike s ome existing QCD sum rule calculations, our results indicate that the form factors have simple dipole or monopole behavior. We obtain result s on the various form factors of the semileptonic decay of D and B mes ons into a light meson and investigate various decay processed such as <(B)over bar (0)> --> pi(+) tau(-) <(nu)over bar (tau)> and <(B)over bar (0)> --> rho(+) tau(-) <(nu)over bar (tau)>. The method allows us to take into account nonperturbative strong interaction effects, there by providing a more reliable determination of the Cabibbo-Kobayashi-Ma skawa matrix elements from the experimental data.