Effect of Non-Orthogonality of Residues in the Wigner-Weisskopf model on   Regeneration for the Neutral $K$ Meson system
  We review the application of the Wigner-Weisskopf model to the two-channel decay problem for the neutral $K$ meson system in the resolvent formalism. The residues in the pole approximation are not orthogonal, leading to additional interference terms in the $K_S-K_L 2\pi$ channel. We show that these terms lead to non-trivial changes in the exit beam in comparison to the result calculated with the assumptions of Lee, Oehme and Yang, and Wu and Yang, corresponding to semigroup evolution for which the pole residues are orthogonal, and hence appear to rule out the applicability of the Wigner-Weisskopf model for the computation of regeneration in the neutral $K$ meson system. 
Eli Cohen, L.P. Horwitz