Low-lying even parity meson resonances and spin-flavor symmetry revisited

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We review and extend the model derived in Phys. Rev. D83 016007 (2011) to address the dynamics of the low-lying even parity meson resonances. This model is based on a coupled channels spin-flavor extension of the chiral Weinberg-Tomozawa Lagrangian. This interaction is then used to study the S-wave meson-meson scattering involving members not only of the π-octet, but also of the ρ-nonet. In this work, we study in detail the structure of the SU(6) symmetry breaking contact terms that respect (or softly break) chiral symmetry. We derive the most general local (without involving derivatives) terms consistent with the chiral symmetry breaking pattern of QCD. After introducing sensible simplifications to reduce the large number of possible operators, we carry out a phenomenological discussion of the effects of these terms. We show how the inclusion of these pieces leads to an improvement of the description of Jᵖ = 2+ sector, without spoiling the main features of the predictions obtained in the original model in the Jᵖ = 0+ and Jᵖ = 1+ sectors. In particular, we find a significantly better description of the Iᵍ(JPC)=0+(2⁺⁺), 1-(2⁺⁺) and the I(Jᵖ)=1/2(2⁺) sectors, which correspond to the f₂(1270), a₂(1320) and K*₂(1430) quantum numbers, respectively.