  We present a simplified and generalized derivation of the flavour-coherent
propagators and Feynman rules for the fermionic kinetic theory based on
coherent quasiparticle approximation (cQPA). The new formulation immediately
reveals the composite nature of the cQPA Wightman function as a product of two
spectral functions and an effective two-point interaction vertex, which
contains all quantum statistical and coherence information. We extend our
previous work to the case of nonzero dispersive self-energy, which leads to a
broader range of applications. By this scheme, we derive flavoured kinetic
equations for local 2-point functions $S^{<,>}_\mathbf{k}(t,t)$, which are
reminiscent of the equations of motion for the density matrix. We emphasize
that in our approach all the interaction terms are derived from first
principles of nonequilibrium quantum field theory.
