Precise analysis of pion-pion scattering data from Roy equations and   forward dispersion relations
  We review our recent analysis of pion-pion scattering data in terms of Roy equations and Forward Dispersion Relations, and present some preliminary results in terms of a new set of once-subtracted coupled equations for partial waves. The first analysis consists of independent fits to the different pion-pion channels that satisfies rather well the dispersive representation. In the second analysis we constrain the fit with the dispersion relations. The latter provides a very precise and model independent description of data using just analyticity, causality and crossing. 
J.R. Pelaez, R. Garcia-Martin, R. Kaminski, F.J. Yndurain