Low-scale leptogenesis in the scotogenic neutrino mass model

Abstract

The scotogenic model proposed by Ernest Ma represents an attractive and minimal example for the generation of small Standard Model neutrino masses via radiative corrections in the dark matter sector. In this paper, we demonstrate that, in addition to neutrino masses and dark matter, the scotogenic model also allows to explain the baryon asymmetry of the Universe via low-scale leptogenesis. First, we consider the case of two right-handed neutrinos (RHNs) N 1;2 , for which we provide an analytical argument why it is impossible to push the RHN mass scale below M min 1 ∼ 10 10 GeV, which is identical to the value in standard thermal leptogenesis in the type-I seesaw scenario with the same washout strength. Then, we present a detailed study of the three-RHN case based on both an analytical and a numerical analysis. In the case of three RHNs, we obtain a lower bound on the N 1 mass of around 10 TeV. Remarkably enough, successful low-scale leptogenesis can be achieved without any degeneracy in the RHN mass spectrum. The only necessary condition is a suppression in the N 1 Yukawa couplings, which results in suppressed washout and a small active neutrino mass of around 10 −12 eV. This leads to the fascinating realization that low-scale leptogenesis in the scotogenic model can be tested in experiments that aim at measuring the absolute neutrino mass scale.

TeV scale leptogenesis with dark matter in non-standard cosmology

“…Successful leptogenesis is possible in this model due to the presence of heavy singlet neutrinos N i whose out-of-equilibrium decay into SM leptons and η can generate the required non-zero lepton asymmetry [49, 50, 53-55, 64, 82]. In the hierarchical spectrum of N i , i = 1 − 3 one can significantly lower the usual Davidson-Ibarra bound to around 10 TeV [49,50] without any need of resonance enhancement [83,84]. Although N 2,3 decay can also generate lepton asymmetry, in principle, we consider the asymmetry generated by N 2,3 decay or any pre-existing asymmetry to be negligible due to strong washout effects mediated either by N 1 or N 2,3 themselves.…”

“…The other contribution to washout W ∆L originates from scatterings which violate lepton number by ∆L = 1, 2. The contribution from ∆L = 2 scatterings η ↔¯ η * , ↔ η * η * is given by [49] W ∆L=2 18…”

“…where z is a complex angle with, z R = z I = m 1 2m 3 [49]. We also consider normal ordering of light neutrino mass with vanishingly small lightest neutrino mass m 1 = 10 −13 eV.…”

Low scale leptogenesis in a hybrid model of the scotogenic type I and III seesaw models

“…This suggests that the lower bound of M N could be 10 4 GeV at least in the present model. j If the relevant parameters j The possibility of low scale leptogenesis in the scotogenic type I seesaw has been intensively studied in [24]. They concluded M N > ∼ 10 4 GeV for the successful leptogenesis just assuming N is in the thermal in the model are fixed at appropriate values which can realize |ε| > ∼ 10 −7 and suppress the washout due to Σ α simultaneously at least for a sufficiently small h N , the low scale leptogenesis could be allowed in this model in a consistent way with the neutrino mass generation, the DM abundance and also the inflation.…”

Trans-Planckian censorship and inflation in grand unified theories

“…At temperatures of O (100) TeV, the baryon asymmetry of the Universe can be produced via thermal leptogenesis [77], provided there is a slight degeneracy in the heavy-neutrino mass spectrum that resonantly enhances the CP asymmetry in heavy-neutrino decays [78][79][80] (see also [81,82] for recent work on resonant leptogenesis). Alternatively, there is a variety of leptogenesis scenarios in the literature that are based on minimal extensions of the simplest type-I seesaw model and that accomplish to successfully generate the baryon asymmetry at temperatures T 100 TeV (see [83,84]…”