The electromagnetic effects in Ke4 decay

The final-state interaction of pions in Ke4 decay allows to obtain the value of the isospin and angular-momentum-zero ππ scattering length a00.We take into account the electromagnetic interaction of pions and isospin-symmetry-breaking effects caused by different masses of neutral and charged pions and estimate the impact of these effects on the procedure of scattering-length extraction from Ke4 decays.