  Neutral kaons, and probably also neutrinos, exhibit oscillations between
flavor eigenstates, as a result of being produced in a superposition of mass
eigenstates. Several recent papers have addressed the question of the energies
and momenta of the components of these states, and their effect on the
coherence of the states and on the wavelength of the oscillations. We point out
that the mass eigenstates need have neither equal momentum nor equal energy,
but can nevertheless be coherent, and that a correct treatment of the
kinematics recovers the usual result for the wavelength of the flavor
oscillations.
