Isospin Breaking in $K\to3\pi$ Decays I: Strong Isospin Breaking
  The CP conserving amplitudes for the decays $K\to3\pi$ are calculated in Chiral Perturbation Theory. The calculation is made at the next-to-leading order including strong and local electromagnetic isospin breaking. A comparison is made between the squared amplitudes with and without isospin violation to estimate the size of the effect. We find corrections of order five percent in the amplitudes. 
Johan Bijnens and Fredrik Borg (Lund)