Related papers: Pion Scalar Form Factor and the Sigma Meson

A new unitarization approach incorporated with chiral symmetry is established and applied to study the $\pi K$ elastic scatterings. We demonstrate that the $\kappa$ resonance exists, if the scattering length parameter in the I=1/2, J=0…

We present a new model independent amplitude analysis of reaction pi(-)p->pi(-) pi(+)n measured at CERN at 17.2 GeV/c on polarized target using a Monte Carlo method for dipion mass 580-1080 MeV. The two solutions for measured moduli…

Recently we obtained the evidence for the existence of sigma(600) meson, which had been sought but missing for a long time, by reanalyzing the I=0 S-wave pi pi scattering phase shift. The sigma-existence was also suggested through the…

The pion-nucleon sigma term ($\sigma_{\pi N}$) is an observable of fundamental importance because embodies information about the internal scalar structure of the nucleon. Nowadays this quantity has triggered renewed interest because it is a…

We apply the perturbative chiral quark model (PCQM) at one loop to analyse meson-baryon sigma-terms. Analytic expressions for these quantities are obtained in terms of fundamental parameters of low-energy pion-nucleon physics (weak pion…

We consider finite volume effects on the electro-magnetic pion form factor near the chiral limit, in the so-called $\epsilon$ regime. The pseudoscalar-vector-pseudoscalar three-point function is calculated in the $\epsilon$ expansion of…

For obtaining the spin space wave function of the pion meson in the light-cone formalism from the naive quark model, it is necessary to take into account Wigner rotation. Consequently there are higher helicity ($\lambda_1+\lambda_2=\pm 1$)…

We have recently completed the one loop calculation of meson-meson scattering within Chiral Perturbation Theory. Once unitarized, these amplitudes provide simultaneously a remarkable description of the resonance region up to 1.2 GeV as well…

The $\sigma$ resonance was observed as a conspicuous $\pi^+\pi^-$ peak in hadronic decays like $J/\psi\to \pi^+\pi^-\omega$ or $D^+\to\pi^+\pi^-\pi^+$. The phase of the $\sigma\to\pi^+\pi^-$ amplitude, extracted from production data within…

The complementarity between Chiral Perturbation Theory and the Linear Sigma Model in the scalar channel is exploited to study $\pi^0\pi^0$ production in $\rho$ and $\omega$ radiative decays, where the effects of a low mass scalar resonance…

Working within the linear sigma model at finite temperature, we construct effective one-loop vertices and propagators satisfying the chiral Ward identities, for small pion momentum and mass compared to the sigma mass. We obtain an expansion…

We study two coupling constants reported as predictions of the sigma model. We obtain an spectral distribution, in terms of the \sigma meson regularized self- energy in one loop order, which is consistently with the Breit-Wigner…

Scalar mesons are a key expression of the infrared regime of QCD. The lightest of these is the $\sigma$. Now that its pole in the complex energy plane has been precisely located, we can ask whether this state is transiently ${\bar q}q$ or…

We derive the pion mass and the elastic pion-pion scattering amplitude in the QCD theta-vacuum up to next-to-leading order in chiral perturbation theory. Using the modified inverse amplitude method, we study the theta-dependence of the mass…

First it is shown that the tree amplitude for pion pion scattering in the minimal linear sigma model has an exact expression which is proportional to a geometric series in the quantity (s-$m_\pi^2$)/($m_B^2-m_\pi^2$), where $m_B$ is the…

I review recent progress made in the description of pion-nucleon scattering, the $\sigma$--term, the scalar form factor and the strangeness content of the nucleon in the framework of heavy baryon chiral perturbation theory. Other topics are…

In this work, we employ a dispersion relation that allows to recover the electromagnetic form factor of the pion from its modulus along the unitarity cut. Unlike the standard dispersive approach, this method extends in a straightforward…

We give some estimates for the light-quark mass dependence of the pole position of the sigma ($f_{0}(500)$) resonance in the complex energy plane, with the help of a chiral Lagrangian for the resonance field and some input from hadronic…

Attention is paid to the production mechanisms of the light scalars that reveal their nature. In the linear sigma model it is revealed the chiral shielding of the \sigma(600) meson and shown that the \sigma field is described by its…

The first part of this report reviews recent developments at the interface between lattice work on QCD with light dynamical quarks, effective field theory and low energy precision experiments. Then I discuss how dispersion theory can be…