Precise determination of the σ pole location from a dispersive analysis

Abstract

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 σ 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 showaremarkable improvement in the precision around the σ region. For practical applications, these results are shown to be very well approximated by a very simple conformal expansion