The ππ S-wave scattering lengths

  title={The ππ S-wave scattering lengths},
  author={Gilberto Colangelo and Juerg Gasser and Heinrich Leutwyler},
Abstract We match the known chiral perturbation theory representation of the ππ scattering amplitude to two loops with a phenomenological description that relies on the Roy equations. On this basis, the corrections to Weinberg's low energy theorems for the S -wave scattering lengths are worked out to second order in the expansion in powers of the quark masses. The resulting predictions, a 0 0 =0.220±0.005, a 0 2 =−0.0444±0.0010, contain remarkably small uncertainties and thus allow a very… CONTINUE READING