Towards a complete theory of thermal leptogenesis in the SM and MSSM

We perform a thorough study of thermal leptogenesis adding finite temperature effects, RGE corrections, scatterings involving gauge bosons and by properly avoiding overcounting on-shell processes. Assuming hierarchical right-handed neutrinos with arbitrary abundancy, successful leptogenesis can be achieved if left-handed neutrinos are lighter than 0.15 eV and right-handed neutrinos heavier than 2 x 10(7) GeV (SM case, 3sigma C.L.). MSSM results are similar. Furthermore, we study how reheating after inflation affects thermal leptogenesis. Assuming that the inflaton reheats SM particles but not directly right-handed neutrinos, we derive the lower bound on the reheating temperature to be T-RH greater than or similar to 2 x 10(9) GeV This bound conflicts with the cosmological gravitino bound present in supersymmetric theories. We study some scenarios that avoid this conflict:,soft leptogenesis', leptogenesis in presence of a large right-handed (s)neutrino abundancy or of a sneutrino condensate. (C) 2004 Elsevier B.V. All rights reserved.