Rare kaon decays

The “golden” kaon decays K⁺ →π⁺ v v and K⁰_I →π⁰ v v offer particularly incisive probes of quark flavor physics. The branching ratios are sensitive to new physics models not easily accessible by other reactions which extend the Standard Model (SM), and the SM predictions are theoretically robust at the several per cent level. Only a precious few accessible second order weak interaction processes involving quarks can be predicted with this level of certainty. Suppression of the branching fractions in the SM to the levels 10^-11 to 10^-10 allows a wide variety of physics beyond the SM at very high mass scales to contribute dramatically to the branching fractions. Experimentally, K⁺ →π⁺ v v and K⁰_I →π⁰ v v, along with many other rare processes, are being pursued vigorously by NA62 at CERN and KOTO at J-PARC, with significant initial observations made of Κ⁺→π⁺ ν ν and stringent limits placed on K⁰_I →π⁰ v v, so far in agreement with SM predictions. The status and prospects for measurements of K⁺ →π⁺ v v and K⁰_I →π⁰ v v will be presented.