Theory prediction of epsilonK

The parameter K plays an important role in the phenomenology of the standard model and its extensions. It is very sensitive to high-energy scales and can be predicted with remarkable precision. I review the theory prediction of K in the standard model, with an emphasis on the theoretical and parametrical uncertainties. In addition, I present the results of our recent NNLO QCD calculation of ηct, the charm-top-quark contribution to the effective |ΔS| = 2 Hamiltonian, leading to |K| = (1.90 ± 0.26) × 10−3.