Sigma pole position and errors of a once and twice subtracted dispersive   analysis of pi-pi scattering data
  We show how the new precise data on kaon decays together with forward dispersion relations, sum rules and once- and twice-subtracted   Roy's equations allow for a precise determination of the sigma meson pole position. We present a comparison and a study of the different sources of uncertainties when using either once- or twice-subtracted Roy's equations to analyze the data. Finally we present a preliminary determination of the sigma pole from the constrained dispersive data analysis. 
R. Kaminski, R. Garcia-Martin, P. Grynkiewicz, J. R. Pelaez