J. R. Pelaez

Meson meson scattering within one loop chiral perturbation theory and its unitarization

We present a complete one-loop calculation of all the two-meson scattering amplitudes within the framework of SU(3) chiral perturbation theory, which includes pions, kaons, and the eta. In addition, we have unitarized these amplitudes with the coupled channel inverse amplitude method, which simultaneously ensures the good low energy properties of chiral perturbation theory and unitarity. We show how this method provides a remarkable description of meson-meson scattering data up to 1.2 GeV including the scattering lengths and the generation of seven light resonances, which is consistent with previous determinations of the chiral parameters. Particular attention is paid to discussing the differences and similarities of this work with previous analyses in the literature.

Precise determination of the f0(600) and f0(980) pole parameters from a dispersive data analysis

We use our latest dispersive analysis of ππ scattering data and the very recent K(ℓ4) experimental results to obtain the mass, width, and couplings of the two lightest scalar-isoscalar resonances. These parameters are defined from their associated poles in the complex plane. The analytic continuation to the complex plane is made in a model-independent way by means of once- and twice-subtracted dispersion relations for the partial waves, without any other theoretical assumption. We find the f(0)(600) pole at (457(-13))+14))-i(279(-7)(+11)) MeV and that of the f(0)(980) at (996 ± 7)-i(25(-6)(+10)) MeV, whereas their respective couplings to two pions are 3.59(-0.13)(+0.11) and 2.3 ± 0.2 GeV.

From controversy to precision on the sigma meson: a review on the status of the non-ordinary

The existence and properties of the sigma meson have been controversial for almost six decades, despite playing a central role in the spontaneous chiral symmetry of QCD or in the nucleon-nucleon attraction. This controversy has also been fed by the strong indications that it is not an ordinary quark-antiquark meson. Here we review both the recent and old experimental data and the model independent dispersive formalisms which have provided precise determinations of its mass and width, finally settling the controversy and leading to its new name:

f_0(500)

f_0(500)

resonance

. We then provide a rather conservative average of the most recent and advanced dispersive determinations of its pole position

Global fit of pi pi and pi K elastic scattering in chiral perturbation theory with dispersion relations.

\sqrt{s_\sigma}=449^{+22}_{-16}-i(275\pm12)

Pion-pion scattering amplitude

. In addition, after comprehensive introductions, we will review within the modern perspective of effective theories and dispersion theory, its relation to chiral symmetry, unitarization techniques, its quark mass dependence, popular models, as well as the recent strong evidence, obtained from the QCD

Strange and nonstrange quark mass dependence of elastic light resonances from SU(3) unitarized chiral perturbation theory to one loop

1/N_c

Remarks on pole trajectories for resonances

expansion or Regge theory, for its non ordinary nature in terms of quarks and gluons.

Inverse amplitude method and Adler zeros

We apply the one-loop results of the SU(3)[sub [ital L]][times]SU(3)[sub [ital R]] chiral perturbation theory supplemented with the inverse-amplitude method to fit the available experimental data on [pi][pi] and [pi][ital K] scattering. With essentially only three parameters we describe accurately data corresponding to six different channels: namely, ([ital I],[ital J])=(0,0), (2,0), (1,1), (1/2, 0), (3/2,0), and (1/2,1). In addition we reproduce the first resonances of the (1,1) and (1/2,1) channel with the right mass corresponding to the [rho] and the [ital K][sup *] (892) particles.