Constraints on the NLO coefficients of the Effective Chiral Lagrangian

Author: Albert Feijoo


Abstract: Chiral Perturbation Theory (ChPT) is an effective theory that has shown to be a powerful tool describing the strong interaction at low energies where a perturbative treatment of QCD results inappropriate due to the large strong coupling. But ChPT is not applicable via a perturbative expansion in a region which contains any resonance. In such cases, one need to resort to non-perturbative resummations. A successful example of this is Unitarized Chiral Perturbation Theory by means of which resonances might be generated dynamically.

This framework provides us with an opportunity to constrain all the parameters which appear in the chiral effective Lagrangian, particularly the next-to-leading order (NLO) coefficients. These parameters are not fixed by the symmetries of the underlying theory (QCD) and, consequently, one needs to fit the models to the available experimental data. With this aim, we have carried out a study of the meson-baryon interaction in the S=-1 sector using a chiral SU(3) Lagrangian up to NLO and implementing unitarization in coupled channels. We have paid a special attention to the K⁻p-->KΞ reactions which are very sensitive to the NLO and Born terms. The stability of the NLO coefficients obtained from our fits is studied by the incorporation of high mass and high spin resonances like Λ(1890), Σ(2030) and Σ(2250). One can extract additional information from further processes in order to discern which models have a more realistic set of fitting parameters associated, for instance, the Λ_b decay.