Kaon mixing and the charm mass

We study contributions to the ΔS = 2 weak Chiral lagrangian producing K0-K̄0 mixing which are not enhanced by the charm mass. For the real part, these contributions turn out to be related to the box diagram with up quarks but, unlike in perturbation theory, they do not vanish in the limit mu → 0. They increase the leading contribution to the KL - KS mass difference by ∼ 10%. This means that short distances amount to (90 ±15)% of this mass difference. For the imaginary part, we find a correction to the λc*2mc2 term of -5% from the integration of charm, which is a small contribution to εK. The calculation is done in the large-Nc limit and we show explicitly how to match short and long distances. © SISSA/ISAS 2004.