The Electromagnetic Mass Differences of Pions and Kaons
  We use the Cottingham method to calculate the pion and kaon electromagnetic mass differences with as few model dependent inputs as possible. The constraints of chiral symmetry at low energy, QCD at high energy and experimental data in between are used in the dispersion relation. We find excellent agreement with experiment for the pion mass difference. The kaon mass difference exhibits a strong violation of the lowest order prediction of Dashen's theorem, in qualitative agreement with several other recent calculations. 
John F. Donoghue (1) and Antonio F. Perez (1 and 2) ((1) University of   Massachusetts Amherst, (2) University of Cincinnati)