The light scalars and the broad sigma(500) in the U3xU3 linear sigma model

Abstract

The lightest scalar and pseudoscalar nonets are discussed within the [A framework of the broken old UxU3 linear sigma model, and it is shown that already at the tree level this model works remarkably well predicting scalar masses and couplings not far from present experimental values, when all parameters are fixed from the pseudoscalar masses and decay constants. The linear sigma model is the simplest way to implement chiral symmetry together with the broken SU3 of the quark model, and this, not well known, success in understanding experiment is comparable to that of the naive quark model for the heavier multiplets. It is argued that this strongly suggest that the light and very broad sigma resonance exists near 500 MeV.