In the absence of new physics in direct detection experiments, the most promising hints of beyond Standard Model physics seem to be offered by flavour physics, which relies on very precise determination of CKM matrix elements. In this work, we provide a new theoretical constraint on the CKM unitarity triangle, which comes from the ratio ε'/ε, i.e. the ratio of direct to indirect CP violation in K → ππ decays. This is the first determination of this quantity from first principles. In addition, I will show the origin of the so-called `∆I = 1/2 rule', which is an observation that KS particle decays predominantly to two pions in an isospin-0 state (as opposed to I=2).
