Recent progress on the light meson resonance description from unitarized Chiral Perturbation Theory and large Nc

Abstract

We present a brief account of the developments in the description of light meson resonances using unitarized extensions of the Chiral Perturbation Theory series, both in energy and temperature. In particular, we describe how these methods have been recently shown to describe simultaneously the low energy and resonance regions of meson-meson scattering. This approach could be of relevance to understand the light scalar mesons since it provides a formalism that respects chiral symmetry and unitarity and is able to generate resonant states without any a priori theoretical bias toward their existence, classification or spectroscopic nature. We will also review how this approach is also able to describe the thermal evolution of the $ρ$ and $σ$ mesons. In addition we review their extensions to higher orders, the most recent determination of the resonance pole properties, as well as their behavior in the large $N_c$ limit, which could be of relevance to understand their spectroscopic nature.

15 pages, Invited talk to the workshop ``Scalar Mesons: an Interesting Puzzle for QCD May 16 - 18, 2003, SUNY Institute of Technology, Utica, New York