Radiative Kaon Decay in Chiral Perturbation Theory
  We analyze the possibility of experimental investigation of new low-energy relations between the values of resonance masses in the meson form factors and the differential rate of radiative kaon decay $K^+\to \pi^+ e^+e^-(\mu^+\mu^- )$ at the current level of the experimental precision. A set of arguments is listed in favour of that these relations can be a consequence of weak static interactions in the Standard Model. 
A.Z. Dubnickova, S. Dubnicka, E. Goudzovski, V.N. Pervushin, M.   Secansky