Heavy-to-light form factors in the final hadron large energy limit of QCD - art. no. 014001

We argue that the large energy effective theory (LEET), originally proposed by Dugan and Grinstein, is applicable to exclusive semileptonic, radiative , and rare heavy-to-light transitions in the region where the energy releas e E is large compared to the strong interaction scale and to the mass of th e final hadron, i.e., for q(2) not close to the zero-recoil point. We deriv e the effective Lagrangian from the QCD one, and show that in the limit of heavy mass M for the initial hadron and large energy E for the final one, t he heavy and light quark fields behave as two-component spinors. Neglecting QCD short-distance corrections, this implies that there are only three for m factors describing all the pseudoscalar to pseudoscalar or vector weak cu rrent matrix elements. We argue that the dependence of these form factors w ith respect to M and E should be factorizable, the M dependence (root M) be ing derived from the usual heavy quark expansion while the E dependence is controlled by the behavior of the light-cone distribution amplitude near th e end point u similar to 1. The usual expectation of the similar to(1 - u) behavior leads to a 1/E-2 scaling law, that is a dipole form in q(2). We al so show explicitly that in the appropriate limit the light-cone sum rule me thod satisfies our general relations as well as the scaling laws in M and E of the form factors, and obtain very compact and simple expressions for th e latter. Finally we note that this formalism gives theoretical support to the quark model-inspired methods existing in the literature. [S0556-2821(99 )02309-7].