The quantum field theory of kaon oscillations

We consider the covariant formulation of kaon mixing in the context of the propagator method. It results important to check the possibility of a sizable effect in the vacuum regeneration of kaons. We discuss all those terms which may give relevant contributions to modify the exponential decay law of the Wigner-Weisskopf narrow-width approximation. Moreover, we examine the characteristic structure of the complex singularities of the matrix propagator and we provide a generalized form of the Bell-Steinberger unitarity sum rule.