Baryogenesis through leptogenesis

Baryogenesis by heavy-neutrino decay and sphaleron reprocessing of both bar yon and lepton number is reconsidered, paying special attention to the flav our structure of the general evolution equations and developing an approxim ate but sufficiently accurate analytic solution to the prototype evolution equation. Two different models of neutrino masses are examined, based on an Abelian U(1) or a non-Abelian U(2) family symmetry. We show that a consist ent picture of baryogenesis can emerge in both cases, although with signifi cant differences. (C) 2000 Elsevier Science B.V. All rights reserved.