  It is shown that the neutrino and neutral kaon oscillation processes can be
consistently described in quantum field theory using only the mass eigenstates
of neutrinos and neutral kaons. The distance-dependent and time-dependent parts
of the amplitudes of these processes are calculated and the results turn out to
be in accord with those of the standard quantum mechanical description of these
processes based on the notion of neutrino flavor states and neutral kaon states
with definite strangeness. However, the physical picture of the phenomena
changes radically: now there are no oscillations of flavor or definite
strangeness states, but, instead of it, there is an interference of amplitudes
due to different virtual mass eigenstates.
