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The importance of N2 leptogenesis

Guy Engelhard, Yuval Grossman, Enrico Nardi, Yosef Nir

hep-pharXiv:hep-ph/0612187

Abstract

We argue that fast interactions of the lightest singlet neutrino N1 would project part of a preexisting lepton asymmetry Lp onto a direction that is protected from N1 washout effects, thus preventing it from being erased. In particular, we consider an asymmetry generated in N2 decays, assuming that N1 interactions are fast enough to bring N1 into full thermal equilibrium. If N1 decays occur at T 109 GeV, that is, before the muon Yukawa interactions enter into thermal equilibrium, then generically part of Lp survives. In this case some of the constraints implied by the standard N1 leptogenesis scenario hold only if Lp ≈ 0. For T 109 GeV, Lp is generally erased, unless special alignment/orthogonality conditions in flavor space are realized.

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