Abstract
The seesaw and leptogenesis commonly depend on the masses of same particles, and thus are both realized at the same scale. In this work, we demonstrate a new possibility to realize a TeV-scale neutrino seesaw and a natural high-scale leptogenesis. We extend the standard model by two gauge-singlet scalars, a vector-like iso-doublet fermion and one iso-triplet Higgs scalar. Our model respects a softly broken lepton number and an exactly conserved $Z_2$ discrete symmetry. It can achieve three things altogether: (i) realizing a testable type-II seesaw at TeV scale with two nonzero neutrino mass-eigenvalues, (ii) providing a minimal inelastic dark matter from the new fermion doublets, and (iii) accommodating a thermal or nonthermal leptogenesis through the singlet scalar decays. We further analyze the current experimental constraints on our model and discuss the implications for the dark matter direct detections and the LHC searches.
Highlights
The seesaw [1,2] extensions of the standard model (SM) naturally explain the tiny neutrino masses [3], while accommodating a leptogenesis [4,5,6] mechanism to generate the observed cosmic baryon asymmetry [3]
Understanding the origins of the neutrino masses, the baryon asymmetry, and the dark matter altogether poses an important challenge to particle physics today
In the conventional seesaw framework, the neutrino mass generation and the leptogenesis for baryon asymmetry are tied to the same high-energy scale
Summary
The seesaw [1,2] extensions of the standard model (SM) naturally explain the tiny neutrino masses [3], while accommodating a leptogenesis [4,5,6] mechanism to generate the observed cosmic baryon asymmetry [3]. Our model has a softly broken lepton number and an exactly conserved Z2 discrete symmetry, so it differs from other models [15] with a spontaneous breaking lepton or baryon number Under such a softly broken lepton number and the exact Z2 symmetry, our model can achieve three things altogether: (i) realizing a testable type-II seesaw at TeV scale with two nonzero neutrino mass eigenvalues; (ii) providing a minimal inelastic dark matter from the new fermion doublets, with the mass-splitting induced by interactions related to the neutrino mass generations; and (iii) accommodating a thermal or inflationary leptogenesis at a high scale through the scalar-singlet decays.
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