P. Colangelo

QCD sum rules, a modern perspective

An introduction to the method of QCD sum rules is given for those who want to learn how to use this method. Furthermore, we discuss various applications of sum rules, from the determination of quark masses to the calculation of hadronic form factors and structure functions. Finally, we explain the idea of the light-cone sum rules and outline the recent development of this approach.

Light scalar mesons in the soft-wall model of AdS/QCD

We study light scalar mesons in the holographic QCD soft-wall model with a background dilaton field. The masses and decay constants are compatible with experiment and QCD determinations if a{sub 0}(980) and f{sub 0}(980) are identified as the lightest scalar mesons; moreover, the states are organized in linear Regge trajectories with the same slope of vector mesons. Comparing the two-point correlation function of scalar operators derived on the anti-de Sitter side and in QCD, information about the condensates can be derived. Strong couplings of scalar states to pairs of light pseudoscalar mesons turn out to be small, at odds with experiment and QCD estimates: we discuss how this discrepancy is related to the description of chiral symmetry breaking in this model, and the possible solutions.

On the light glueball spectrum in a holographic description of QCD

We investigate the spectra of light scalar and vector glueballs in a holografic description of QCD with a dilaton background bulk field. In particular, we study how the glueball masses depend on the conditions on the dilaton background and on the geometry of the bulk.

Using heavy quark spin symmetry in semileptonic

The form factors parameterizing the B_c semileptonic matrix elements can be related to a few invariant functions if the decoupling of the spin of the heavy quarks in B_c and in the mesons produced in the semileptonic decays is exploited. We compute the form factors as overlap integral of the meson wave-functions obtained using a QCD relativistic potential model, and give predictions for semileptonic and non-leptonic B_c decay modes. We also discuss possible experimental tests of the heavy quark spin symmetry in B_c decays.

B_c

The BaBar measurements of the ratios

decays

{\cal R}(D^{(*)})=\frac{{\cal B}(B \to D^{(*)} \tau {\bar \nu}_\tau)}{{\cal B}(B \to D^{(*)} \mu {\bar \nu}_\mu)}

On the anomalous enhancement observed in

deviate from the standard model expectation, while new results on the purely leptonic

B \to D^{(*)}\tau{\bar \nu}_\tau

B \to \tau {\bar \nu}_\tau

decays

mode show a better consistency with the standard model, within the uncertainties. In a new physics scenario, one possibility to accomodate these two experimental facts consists in considering an additional tensor operator in the effective weak hamiltonian. We study the effects of such an operator in a set of observables, in semileptonic

New meson spectroscopy with open charm and beauty

B \to D^{(*)}