Theoretical status of ${\epsilon }^{\prime }/\epsilon$

Abstract

We briefly overview the historical controversy around Standard Model predictions of ${\epsilon }^{\prime }/\epsilon$ and clarify the underlying physics. A full update of this important observable is presented, with all known short- and long-distance contributions, including isospin-breaking corrections. The current Standard Model prediction, $\mathrm{Re}({\epsilon }^{\prime }/\epsilon )=(14\pm 5)\cdot 10^{-4}$, is in excellent agreement with the experimentally measured value.

Invited talk at Kaon 2019 (Perugia, 10-13 September 2019). 6 pages, 3 figures