Theoretical Status of epsilon'/epsilon

Abstract

We review the present theoretical status of the CP violating ratio epsilon'/epsilon 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 m_s, B_6^(1/2), B_8^(3/2), \Lambda_MSbar and Omega_{\eta+\eta'}. While the sign and the order of magnitude of SM estimates for epsilon'/epsilon agree with the data, for central values of these parameters most estimates of epsilon'/epsilon in the SM are substantially below the grand experimental average (21.2\pm 4.6)\cdot 10^{-4}. Only in a small corner of the parameter space can epsilon'/epsilon 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 epsilon'/epsilon indicate new physics. A brief discussion of epsilon'/epsilon beyond the Standard Model is presented.