QCD radiative corrections to upsilon decay into scalar plus gamma and pseudoscalar plus gamma

The calculation is presented of the α_S correction to heavy quarkonium decay into scalar and pseudoscalar plus gamma. For the scalar case, the result agrees with the value previously calculated by Vysotsky. In both cases the correction brings about a substantial reduction in the rate.     

New approach to axial coupling constants in the QCD sum rule

We derive new QCD sum rules for the axial coupling constants by considering the correlation functions of axial-vector currents in a one-nucleon state. The QCD sum rules tell us that the axial coupling constants are expressed by nucleon matrix elements of quark-gluon composite operators which are related to the sigma terms and the moments of parton distributions. The results for the isovector axial coupling constants and the eighth component of the SU(3)(f) octet are in good agreement with experiment.     

Exclusive radiativeB-decays in the light-cone QCD sum rule approach

We discuss vector, axial-vector, scalar and pseudoscalar two-point functions at low and intermediate energies. We first review what is known from chiral perturbation theory, as well as from a heat kernel expansion within the context of an extended Nambu-Jona-Lasinio (ENJL) model. We derive then these two-point functions to all orders in the momenta and to leading order in 1/N _c within the framework of this model. We find an improved high-energy behaviour and a general way of parametrizing them that shows relations between some of the two-point functions, which are also valid in the presence of gluonic interactions. The similarity between the shape of the experimentally known spectral functions and the ones we derive, is greatly improved with respect to those predicted by the usual constituent quark like models. We also obtain the scalar massM _s =2M _Q independent of the regularization scheme. In the end, we calculate fully an example of a nonleptonic matrix element in the ENJL-model, theπ ⁺?π ⁰ electromagnetic mass difference and find good agreement with the measured value.

     

The QCD sum rule approach for the semileptonic decay of the D or B meson into a light meson and leptons

We use the method of QCD sum rules to treat the semileptonic weak decay of the D or B meson into a light meson and leptons. To obtain the transition form factors, we adopt the two-point Green’s function in the presence of an external vector or axial-vector field. We find that this method can be related approximately to the traditional three-point Green’s function in the heavy quark limit (m _Q → ∞). Unlike some existing QCD sum rule calculations, our results indicate that the form factors have simple dipole or monopole behavior. We obtain results on the various form factors of the semileptonic decay of D and B mesons into a light meson and investigate various decay processes such as B?⁰ → π ⁺ τ _^?ν?_τ and B?⁰ → ρ ⁺ τ^～ν?_τ. The method allows us to take into account nonperturbative strong interaction effects, thereby providing a more reliable determination of the Cabibbo-Kobayashi-Maskawa matrix elements from the experimental data.