Aspects of High Scale Leptogenesis with Low-Energy Leptonic CP Violation

Using the density matrix equations (DME) for high scale leptogenesis based on the type I seesaw mechanism, in which the CP violation (CPV) is provided by the low-energy Dirac or/and Majorana phases of the neutrino mixing (PMNS) matrix, we investigate the 1-to-2 and the 2-to-3 flavour regime transitions, where the 1, 2 and 3 leptogenesis flavour regimes in the generation of the baryon asymmetry of the Universe (BAU) are described by the Boltzmann equations. Concentrating on the 1-to-2 flavour transition we determine the general conditions under which the BAU goes through zero and changes sign in the transition. Analysing in detail the behaviour of the BAU in the transition in the case of two heavy Majorana neutrinos with hierarchical masses we find, in particular, that i) the Boltzmann equations in many cases fail to describe correctly the generation of the BAU in the 1, 2 and 3 flavour regimes, ii) the 2-flavour regime can persist above (below) ∼1e12 GeV (∼1e9 GeV), iii) the flavour effects in leptogenesis persist beyond the typically considered maximal for these effects leptogenesis scale of 1e12 GeV. We further determine the minimal scale at which we can have successful leptogenesis when the CPV is provided only by the Dirac or Majorana phases of the PMNS matrix as well as the ranges of scales and values of the phases for having successful leptogenesis. We show, in particular, that when the CPV is due to the Dirac phase δ, there is a direct relation between the sign of sin(δ) and the sign of the BAU in the regions of viable leptogenesis in the case of normal hierarchical light neutrino mass spectrum; for the inverted hierarchical spectrum the same result holds for mass scales below 1e13 GeV. The considered different scenarios of leptogenesis are testable and falsifiable in low-energy neutrino experiments