Radiative modes K ⁺ → π ⁺ γ ^* γ ^(*) and the K⁺ → π+4e decay

Abstract We discuss radiative transitions of a kaon to pion and two photons. In particular, we have a closer look at radiative corrections for the K + → π + ℓ + ℓ − decays and present the branching ratio of the K + → π + e + e − e + e − process calculated for the first time at leading order in the Standard Model.