Decay Spectrum of $K^+ \to e^+ \nu_{e}\gamma$
  The form factors of the $K^+ \to \gamma$ transition are studied in the light-front quark model and chiral perturbation theory of $O(p^6)$. The decay spectrum of $K^+ \to e^+ \nu_{e}\gamma$, dominated by the structure dependent contribution, is illustrated in both models. 
C.H. Chen, C.Q. Geng and C.C. Lih