Leptonic and Semilepi’onic D-decays from Qcd Sum Rules

Leptonic and semileptonic decay amplitudes play a key role for a determination of the K&l quark mixing matrix as well as for a test of a wide variety of theoretical predictions on heavy flavour weak transitions. Thus considerable effort has been devoted to the theoretical estimates of the leptonic constant fD (and fB) and of the D13 (and B13) decay form factors. Here we will briefly present some results on these transitions, which have been obtained in the framework of QCD sum rules [ 1,2]. To just outline the main points of this formalism, in the version of finite energy sum rules (FESR) particularly convenient to the issue here, we recall that the starting objects are the current correlators qQ2>=i J d4x eiqx <vacl TJ(x)J(o)+lvao, (1)