Precise dispersive data analysis of the f_0(600) pole

We review how the use of recent precise data on kaon decays together with forward dispersion relations (FDR) and Roy’s equations allow us to determine the sigma resonance pole position very precisely, by using only experimental input. In addition, we present preliminary results for a modified set of Roy-like equations with only one subtraction, that show a remarkable improvement in the precision around the σ region. We also improve the matching between the parametrizations at low and intermediate energy of the S0 wave, and show that the effect of this on the sigma pole position is negligible