Time-to-space conversion in quantum field theory of flavor mixing
  We consider the problem of time-to-space conversion in quantum field theory of flavor mixing using a generalization of the wave-packet method in quantum mechanics. We work entirely within the canonical formalism of creation and annihilation operators that allows us, unlike the usual wave-packet formulation, to include the nontrivial effect due to flavor condensation in the vacuum. 
Chueng-Ryong Ji and Yuriy Mishchenko