Meson resonances from unitarized meson scattering at one loop in Chiral Perturbation Theory

We show the results for the scattering poles associated to the ρ, f 0 , a 0 , K * , σ and κ resonances in meson-meson scattering. Our amplitudes are obtained from the complete one-loop meson-meson scattering amplitudes from Chiral Perturbation Theory. Once unitarized with the Inverse Amplitude Method, they describe remarkably well the data simultaneously in the low energy and resonance regions up to 1.2 GeV, using low energy parameters compatible with present determinations. We report on our progress [1] on determining the poles that appear in the recent description [2] of meson-meson scattering by means of unitarized one-loop Chiral Perturbation Theory (ChPT). The interest of these poles is that, at least when they are close to the real axis, they are associated to Breit-Wigner resonances whose mass M R and width Γ R is related to the pole position as √ s pole ≃ M R − Γ R /2. When they are not so close to the real axis, their interpretation is much less clear. Starting from one-loop Chiral Perturbation Theory [3] our unitarized amplitudes respect the spontaneous chiral symmetry pattern of QCD up to fourth order in the chiral expansion, i.e. in powers of meson masses or momenta over the chiral scale 4πf ≃ 1.2 GeV. Nevertheless, since the ChPT amplitudes behave as polynomials at high energy, they violate partial wave unitarity, which we impose with the Inverse Amplitude Method (IAM). Part of this program had already been carried first for partial waves in the elastic region, for which a single channel approach could be used, finding the ρ and σ poles in ππ scattering and that of K * in πK → πK [4]. For coupled channel processes, an approximate form of this approach had already been shown [5] to yield a remarkable description of meson-meson scattering up to 1.2 GeV. When these partial waves were continued to the second Riemann sheet of the complex s several poles were found, corresponding to the