$\varepsilon'/\varepsilon$ in and beyond the Standard Model

Abstract

Estimates of the CP violating observable $\varepsilon'/\varepsilon$ have gained some attention in the past few years. Depending on the long-distance treatment used, they exhibit up to $2.9\sigma$ deviation from the experimentally measured value. Such a deviation motivates the investigation of New Physics (NP) effects in the process $K\to\pi\pi$. In my talk I will review the Standard Model (SM) prediction for $\varepsilon'/\varepsilon$, with a special focus on the Dual QCD approach. On the NP side, I will discuss a recent computation of the hadronic matrix elements of NP operators. Furthermore a master formula for BSM effects in $\varepsilon'/\varepsilon$ is presented. Finally, a treatment of $\varepsilon'/\varepsilon$ using the SM effective theory (SMEFT) will be discussed together with possible correlations to other observables.