2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/203435The first part of this report reviews recent developments at the interface between lattice work on QCD with light dynamical quarks, effective field theory and low energy precision experiments. Then I discuss how dispersion theory can be used to analyze the low energy structure of the $ππ$ scattering amplitude in a model independent manner. This leads to an exact formula for the mass and width of the lowest few resonances, in terms of observable quantities. As an application, I consider the pole position of the $σ$, paying particular to error propagation in the numerical analysis. The report is based on work done in collaboration with Irinel Caprini and Gilberto Colangelo.10 pages, 4 figures, Contribution to the proceedings of the Workshop on Scalar Mesons and Related Topics, honouring the 70th birthday of Michael Scadron, Lisbon, Portugal, Feb. 11-16, 2008High Energy Physics - Phenomenologytext