Chiral Ward identities lead to consistent accounting for the sigma's width in the linear sigma model's Feynman rules. Reanalysis of pion scattering data at threshold imply a mass for the sigma of 600+ 200 - 100 MeV.
@article{arxiv.hep-ph/9904224,
title = {Pion Scattering Revisited},
author = {M. Ruiz-Altaba and J. L. Lucio and M. Napsuciale},
journal= {arXiv preprint arXiv:hep-ph/9904224},
year = {2009}
}