I don't understand why the propagation of neutrino mass eigenstates are given by planewave solutions as expressed in this Wikipedia article.
In addition to not being used to thinking in the Schrodinger picture when it comes to quantum field theories, I think I'm misunderstanding what 'mass eigenstates' and 'flavor eigenstates' mean. By 'mass eigenstates' I presume that they mean that these are eigenstates of the free neutrino theory. Then the flavor eigenstates are eigenstates of the electro-weak theory, I think without the interaction with the charged leptons.
But, given this understanding, I'm not sure why the mass eigenstates propagate as planewaves instead of as something much more complicated because they are not eigenstates of the interacting Hamiltonian.