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The counterterm combination that describes the decay of pseudoscalar mesons into charged lepton pairs at lowest order in chiral perturbation theory is considered within the framework of QCD in the limit of a large number of colours Nc. When further restricted to the lowest meson dominance approximation to large-Nc QCD, our results agree well with the available experimental data.
In this work, we calculate the branching ratios for the $eta(eta)rightarrowbar{ell}ell$ decays, where $ell = e,mu$. These processes have tiny rates in the standard model due to spin flip, loop, and electromagnetic suppression, for what they could be
The masses of the negative parity 70-plet baryons are analyzed in large N_c QCD to order 1/N_c and to first order in SU(3) symmetry breaking. The existing experimental data are well reproduced and twenty new observables are predicted. The leading ord
We show that the nonperturbative solution of the SU(2) linear sigma model field theory requires color number Nc=3. Also, we show that the three-point and four-point functions bootstrap (or nonperturbatively ``shrink) in the chiral limit to the tree a
The structure of the 1/Nc expansion for the baryon distribution amplitude in QCD is tested using quark models. Earlier conjectures about this structure based on the evolution equation and on the soft-pion theorem are confirmed by the model analysis.
We present new results for the matrix elements of the Q_6 and Q_4 penguin operators, evaluated in a large-Nc approach which incorporates important O(N_c^2frac{n_f}{N_c}) unfactorized contributions. Our approach shows analytic matching between short-