NEUTRAL HEAVY-LEPTONS AND ELECTROWEAK BARYOGENESIS

We investigate the possibility that baryogenesis occurs during the wea k phase transition in a minimal extension of the Standard Model which contains extra neutral leptons and conserves total lepton number. The necessary CP-violating phases appear in the leptonic Yukawa couplings, We compute the CP asymmetries in both the neutral and the charged lep ton fluxes reflected in the unbroken phase. Using present experimental bounds on the mixing angles and Standard Model estimates for the para meters related to the scalar potential, we conclude that it seems unli kely to produce the observed baryon to entropy ratio within this kind of models. However, we comment on the possibility that the constraints on the mixings might be naturally relaxed due to small finite tempera ture effects. (C) 1997 Elsevier Science B.V.