Degenerate minimal see-saw and leptogenesis

We analyze the most general version of the supersymmetric minimal see-saw model with only two right-chiral neutrinos which are degenerate in masses at the scale of Grand Unification. We study the renormalization effects that give rise to non-zero CP asymmetries in the decays of these neutrinos and find that their resonant enhancement due to small mass splitting is partly compensated by other RG effects in the running of the neutrino Yukawa couplings. In spite of this compensation, the CP asymmetries can be large enough for successful thermal leptogenesis. Moreover, they depend very weakly on the right-chiral neutrino masses and the resulting leptogenesis can be successful for very low reheating temperature, thereby allowing to overcome the gravitino problem. (C) 2004 Elsevier B.V. All rights reserved.