$\varepsilon'/\varepsilon$ in the Standard Model and Beyond: 2021

Abstract

The present status of the ratio ε /ε in the Standard Model (SM) is summarized. In particular we stress the differences between three approaches that attempt to calculate ε /ε within the SM: Lattice QCD, Dual QCD and Chiral Perturbation Theory. As presently there is still a significant room left for new physics (NP) contributions, we summarize the present status of the technology that has been recently developed with the goal to analyze ε /ε and its correlations with other observables within the Weak Effective Theory (WET) and the Standard Model Effective Field Theory (SMEFT). We also make a few comments on the interpretation of the main dynamics behind the ∆I = 1/2 rule in K → ππ decays.