Comparison of Lattice and Chiral Perturbation Theory calculations of   pion scattering lengths
  I compare the lattice calculation of Fukugita et al. for the pion S-wave scattering lengths to the predictions of Chiral Perturbation Theory to two loop accuracy. I find good agreement, despite the use of the quenched approximation in the lattice calculation. 
Gilberto Colangelo