The Scalar q bar q nonet and Confirmation of the broad sigma meson
  The available data on the a0(980), f0(980), f0(1300) and K*0(1430) mesons are fitted as a distorted 0++ nonet using only 6 parameters and a very general model. This includes all light two-pseudoscalar thresholds, constraints from Adler zeroes, flavour symmetric couplings, unitarity and physically acceptable analyticity. One finds that with the large overall coupling there can appear two physical resonance poles from only one q bar q state. Thus the f0(980) and f0(1300) resonance poles are two manifestations of the same s bar s state. On the other hand, the u bar u state, when unitarized and strongly distorted by hadronic mass shifts, becomes an extremely broad Breit-Wigner-like background, with its pole at s =(0.158-i0.235) GeV^2. This is the sigma meson required by models for spontaneous breaking of chiral symmetry. 
Nils Tornqvist