We study the possibility of generating the observed baryon asymmetry via
leptogenesis in the decay of heavy Standard Model singlet fermions which carry
lepton number, in a framework without Majorana masses above the electroweak
scale. Such scenario does not contain any source of total lepton number
violation besides the Standard Model sphalerons, and the baryon asymmetry is
generated by the interplay of lepton flavour effects and the sphaleron
decoupling in the decay epoch.Comment: V2 (published version): 21 pages, 4 figures. Some explanations have
been adde
