Electroweak naturalness in three-flavour Type I see-saw and implications for leptogenesis

Abstract

In the Type I see-saw model, the naturalness requirement that corrections to the electroweak $\mu$ parameter not exceed 1 TeV results in a rough bound on the lightest right-handed neutrino mass, $M_{N_1}\lesssim 3\times 10^7$ GeV. In this letter we derive generic bounds applicable in any three-flavour Type I see-saw model. We find $M_{N_1}\lesssim 4\times 10^7$ GeV and $M_{N_2}\lesssim 7\times 10^7$ GeV. In the limit of one massless neutrino, there is no naturalness bound on $M_{N_3}$ in the Poincare protected decoupling limit. Our results confirm that no Type I see-saw model can explain the observed neutrino masses and baryogenesis via hierarchical ($N_1$-, $N_2$-, or $N_3$-dominated) thermal leptogenesis while remaining completely natural.

4 pages, 3 figures, v2 minor changes

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• Heavy Dark Matter, Neutrino Masses and Higgs Naturalness from a Strongly Interacting Hidden Sector
• Purely Triplet Seesaw and Leptogenesis within Cosmological Bound, Dark Matter and Vacuum Stability
• Searching for radiative neutrino mass generation at the LHC
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• Leptogenesis from a $U(1{)}_D$ resonance