A case of subdominant/suppressed "high energy" contribution to the baryon asymmetry of the Universe in flavoured leptogenesis

The CP-violation necessary for the generation of the baryon asymmetry of the Universe YB in the "flavoured" leptogenesis scenario can arise from the "low energy" PMNS neutrino mixing matrix U and/or from the "high energy" part of neutrino Yukawa couplings, which can mediate CP-violating phenomena only at some high energy scale. The possible interplay between these two types of CP-violation is analysed. The type I see-saw model with three heavy right-handed Majorana neutrinos having hierarchical spectrum is considered. We show that in the case of inverted hierarchical light neutrino mass spectrum, there exist regions in the corresponding leptogenesis parameter space where the relevant "high energy" phases have large CP-violating values, but the purely "high energy" contribution in YB plays a subdominant role in the production of baryon asymmetry compatible with the observations. In some of these regions the purely "high energy" contribution in YB is so strongly suppressed that one can have successful leptogenesis only if the requisite CP-violation is provided by the Majorana phase(s) in the neutrino mixing matrix. © 2008 Elsevier B.V. All rights reserved.