We introduce four-point functions in the hadronic ladder resummation approach to large Nc QCD Green functions. We determine the relevant one to calculate the BK kaon parameter in the chiral limit. This four-point function contains both the large momenta QCD OPE and the small momenta ChPT at NLO limits, analytically. We get B^Kχ=0.38±0.15. We also give the ChPT result at NLO for the relevant four-point function to calculate BK outside the chiral limit, while the leading QCD OPE is the same as the chiral limit one.
Cite
@article{arxiv.hep-ph/0601197,
title = {The $B_K$ Kaon Parameter in the Chiral Limit},
author = {Johan Bijnens and Elvira Gamiz and Joaquim Prades},
journal= {arXiv preprint arXiv:hep-ph/0601197},
year = {2009}
}