Theoretical Status of ε′/ε

We review the present theoretical status of the CP violating ratio ε/ε in the Standard Model (SM) and confront its estimates with the most recent data. In particular we review the present status of the most important parameters ms, B (1/2) 6 , B (3/2) 8 , Λ (4) MS and Ωη+η′ . While the sign and the order of magnitude of SM estimates for ε/ε agree with the data, for central values of these parameters most estimates of ε/ε in the SM are substantially below the grand experimental average (21.2 ± 4.6) · 10−4. Only in a small corner of the parameter space can ε/ε in SM be made consistent with experimental results. In view of very large theoretical uncertainties, it is impossible to conclude at present that the data on ε/ε indicate new physics. A brief discussion of ε/ε beyond the Standard Model is presented. Invited talk given at KAON 99 Chicago, June 21-26, 1999