Chiral Low-Energy Constants: Status and Prospects

Chiral low-energy constants (LECs) carry the information of short-distance dynamics involving heavier degrees of freedom not present in the chiral Lagrangian. Our knowledge of the LECs is all-important at phenomenological level because their relevance in the prediction of hadronic observables at low-energies and on the other side because they provide hints on the construction of a dual theory of QCD in the low-energy regime. I review briefly the status of these important couplings.Comment: 7 pages. Talk given at the 31st International Conference of Theoretical Physics, 5-11 Sep 2007, Ustron (Katowice, Poland

Hadronic decays of the tau lepton: Theoretical outlook

The structure of the form factors stemmed from the hadronization of QCD currents in the energy region of the resonances can be explored through the analyses of exclusive hadronic decays of the tau lepton. I give a short review on the later theoretical progress achieved in the description of experimental data.Comment: 13 pages, 5 figures. Talk given at the 9th International Workshop on Tau Lepton Physics, TAU06, 19th-22nd September 2006, Pisa (Italy). Error in the text corrected. Settings and conclusions unchange

Large-Nc estimate of the chiral low-energy constants

Chiral low-energy constants incorporate short-distance information from the dynamics involving heavier degrees of freedom not present in the chiral Lagrangian. We have studied the contribution of the lightest resonances to the chiral low-energy constants, up to O(p^6), within a systematic procedure guided by the large-Nc limit of QCD and also including short-distance asymptotic constraints.Comment: 8 pages, 1 figure. Talk given at the Final Euridice Meeting "Effective Theories of colours and flavours : from EURODAPHNE to EURIDICE", 24th-27th August 2006, Kazimierz (Poland

Semileptonic decays of charmed mesons in the effective action of QCD

Within the framework of phenomenological Lagrangians we construct the effective action of QCD relevant for the study of semileptonic decays of charmed mesons. Hence we evaluate the form factors of D -> P(0^-) l^+ nu_l at leading order in the 1/N_C expansion and, by demanding their QCD-ruled asymptotic behaviour, we constrain the couplings of the Lagrangian. The features of the model-independent parameterization of form factors provided and their relevance for the analysis of experimental data are pointed out.Comment: 1+24 pages, 1 figure. Updated version. Conclusions unchanged. Accepted for publication in The European Physical Journal

New contributions to heavy quark sum rules

We analyse new contributions to the theoretical input in heavy quark sum rules and we show that the general theory of singularities of perturbation theory amplitudes yields the method to handle these specific features. In particular we study the inclusion of heavy quark radiation by light quarks at O(alpha_s^2) and non-symmetric correlators at O(alpha_s^3). Closely related, we also propose a solution to the construction of moments of the spectral densities at O(alpha_s^3) where the presence of massless contributions invalidates the standard approach. We circumvent this problem through a new definition of the moments, providing an infrared safe and consistent procedure.Comment: 15 pages, 3 figures. Version accepted for publication in The European Journal of Physics C; several new comments and references added, conclusions unchange