Kadanoff-Baym Approach to Flavour Mixing and Oscillations in Resonant
  Leptogenesis
  We describe a loopwise perturbative truncation scheme for quantum transport
equations in the Kadanoff-Baym formalism, which does not necessitate the use of
the so-called Kadanoff-Baym or quasi-particle ansaetze for dressed propagators.
This truncation scheme is used to study flavour effects in the context of
Resonant Leptogenesis (RL), showing explicitly that, in the weakly-resonant
regime, there exist two distinct and pertinent flavour effects in the
heavy-neutrino sector: (i) the resonant mixing and (ii) the oscillations
between different heavy-neutrino flavours. Moreover, we illustrate that
Kadanoff-Baym and quasi-particle ansaetze, whilst appropriate for the
flavour-singlet dressed charged-lepton and Higgs propagators of the RL
scenario, should not be applied to the dressed heavy-neutrino propagators. The
use of these approximations for the latter is shown to capture only flavour
oscillations, whilst discarding the separate phenomenon of flavour mixing.
