Pi Pi Scattering and Scalar Mesons in an Effective Chiral Lagrangian
  In this talk I summarize recently proposed mechanisms to understand pi pi scattering to 1 GeV in an effective chiral Lagrangian. The Lagrangian includes higher resonances in addition to pions consistently with the chiral symmetry. Iso-spin zero S-wave partial wave amplitude is reproduced up till about 1.2 GeV by including a pion self-interaction and resonant pole exchanges of rho, f0(980) and sigma derived from the effective chiral Lagrangian. The best fit shows that sigma has a mass of around 560 MeV and a width of about 370 MeV. 
Masayasu Harada