No abstract

The baryon axial vector current is computed at one-loop order in large-Nc baryon chiral perturbation theory, where Nc is the number of colors. Loop graphs with octet and decuplet intermediate states are systematically incorporated into the analysis and the effects of the decuplet-octet mass difference and SU(3) flavor symmetry breaking are accounted for. As expected, large-Nc cancellations between different one-loop graphs are observed as a consequence of the large-Nc spin-flavor symmetry of QCD baryons. Fitting our analytical formulas against experimental data on baryon semileptonic decays and the strong decays of decuplet baryons, a detailed numerical analysis regarding the determination of the basic parameters of large-Nc baryon chiral perturbation theory as well as the extraction of the baryon axial vector couplings is performed. The large-Nc baryon chiral perturbation theory predictions are in very good agreement both with the expectations from the 1/Nc expansion and with the experimental data.

We obtain limits on the electromagnetic and weak dipole moments of the tau-lepton in the framework of a Left-Right symmetric model (LRSM) and a class of E 6 inspired models with an additional neutral vector boson Z θ . Using as an input the data obtained by the L3 and OPAL Collaborations for the reaction e + e − → τ + τ − γ, we get a stringent limit on the LRSM mixing angle φ, −1.66 × 10 −3 < φ < 1.22 × 10 −3 , which in turn induces bounds on the tau weak dipole moments which are consistent with the bounds obtained recently by the DELPHI and ALEPH Collaborations from the reaction e + e − → τ + τ − . We also get similar bounds for the weak dipole moments of the tau lepton in the framework of E 6 superstring models.

No abstract