Violations of Dashen's Theorem

Abstract

The electromagnetic contribution to the $K^{+}-K^0$ mass difference is calculated in the $1/N_c$ 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 $1/N_c$ approach by Bardeen et al. Relatively large corrections are found.

Comments: Revised version, Latex, 10 pages, 4 figures, 2 included, NORDITA 93/15 N,P. Numerical mistake in evaluation of long-distance corrected and comparison with UMHEP-376 by Donoghue et al. added