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

摘要

Four of the six parameters defining the two-loop pi pi scattering amplitude have been determined using Roy dispersion relations. Combining this information with the Standard chi PT expressions, we obtain the threshold parameters, low-energy phases and the O(p(4)) constants l(1)(r), l(2)(r). The result l(2)(r)(M-rho) = (1.6 +/- 0.4 +/- 0.9) x 10(-3) ((l) over bar(2) = 4.17 +/- 0.19 +/- 0.43) reproduces the correct D-waves but it is incompatible with existing Standard chi PT analyses of K-14 form factors beyond one loop. (C) 1997 Elsevier Science B.V.