Determination of SU(2) Chiral Perturbation Theory low energy constants   from a precise description of pion-pion scattering threshold parameters
  We determine the values of the one- and two-loop low energy constants appearing in the SU(2) Chiral Perturbation Theory calculation of pion-pion scattering. For this we use a recent and precise sum rule determination of some scattering lengths and slopes that appear in the effective range expansion. In addition we provide sum rules for these coefficients up to third order in the expansion. Our results when using only the scattering lengths and slopes of the S, P, D and F waves are consistent with previous determinations, but seem to require higher order contributions if they are to accommodate the third order coefficients of the effective range expansion. 
J. Nebreda, J. R. Pelaez and G. Rios
hep-ph hep-lat