Violations of Dashen's theorem
The electromagnetic contribution to the K+-K0 mass difference is calculated in the 1 Nc approach including the SU(3) breaking contributions due to a non-zero strange quark mass. The short-distance contribution can be unambiguously determined in terms of the known parameters of the next-to-leading order chiral Lagrangian. The long distance part is estimated using the 1 Nc approach by Bardeen et al.