Determination of <(pi pi)I=2/ohm 7,8/K0 > in the chiral limit

We reconsider the dispersive evaluation of the weak matrix elements <(pi pi )(I=2) /Q(7.8) /K-0> in the chiral limit. The perturbative matching is acco mplished fully within the scheme dependence used in the two loop weak OPE c alculations. The effects of dimension eight (and higher dimension) operator s are fully accounted for. We perform a numerical determination of the weak matrix elements using our dispersive sum rules fortified by constraints fr om the classical chiral sum rules. A careful assessment of the attendant un certainties is given. (C) 2001 Elsevier Science B.V. All rights reserved.