Comment on the prediction of two-loop standard chiral perturbation theory for low-energy ππ scattering

Four of the six parameters defining the two-loop ππ scattering amplitude have been determined using Roy dispersion relations. Combining this information with the Standard χPT expressions, we obtain the threshold parameters, low-energy phases and the O(p4) constants l1r, l2r. The result l2r(Mp) = (1.6 ± 0.4 ± 0.9) × 10−3 (l2 = 4.17 ± 0.19 ± 0.43) reproduces the correct D-waves but it is incompatible with existing Standard χPT analyses of K14 form factors beyond one loop.