The Quantum Field Theory of the Kaon Oscillations

We consider the covariant formulation of the 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.