Abstract
Contrary to the common lore based on naive dimensional analysis, the seesaw scale for neutrino masses can be naturally in the TeV range, with small parameters coming from radiative corrections. We present one such class of type-I seesaw models, based on the left-right gauge group SU(2)L × SU(2)R × U(1)B-L realized at the TeV scale, which fits the observed neutrino oscillation parameters as well as other low energy constraints. We discuss how the small parameters of this scenario can arise naturally from one loop effects. The neutrino fits in this model use quasi-degenerate heavy Majorana neutrinos, as also required to explain the matter-antimatter asymmetry in our Universe via resonant leptogenesis mechanism. We discuss the constraints implied by the dynamics of this mechanism on the mass of the right-handed gauge boson in this class of models with enhanced neutrino Yukawa couplings compared to the canonical seesaw model and find a lower bound of mWR ≥ 9.9 TeV for successful leptogenesis assuming maximal CP asymmetry for each flavor. We also present a model with explicit neutrino mass fit, where the lower bound goes up to 13.1 TeV due to less than maximal primordial CP asymmetry predicted by the model.
Highlights
The seesaw mechanism [1] seems to provide a simple way to understand the smallness of neutrino masses
Contrary to the common lore based on naive dimensional analysis, the seesaw scale for neutrino masses can be naturally in the TeV range, with small parameters coming from radiative corrections
We discuss the constraints implied by the dynamics of this mechanism on the mass of the right-handed gauge boson in this class of models with enhanced neutrino Yukawa couplings compared to the canonical seesaw model and find a lower bound of mWR ≥ 9.9 TeV for successful leptogenesis assuming maximal CP asymmetry for each flavor
Summary
The seesaw mechanism [1] seems to provide a simple way to understand the smallness of neutrino masses. The attractive aspect of this mechanism is that the same Yukawa couplings Yν that give rise to neutrino masses via the seesaw mechanism in Eq (1) are responsible for the origin of matter, implying an intimate connection between two seemingly disparate pieces of evidence for beyond the SM physics This beautiful idea can be tested, provided the seesaw scale, and the scale at which leptogenesis takes place, is accessible to current and near future laboratory experiments. Through a detailed analysis of the relevant Boltzmann equations, it was concluded in [21] that even for maximal CP -asymmetry ε ∼ O(1), the observed value of the baryon asymmetry can be explained by leptogenesis in these L-R models, only if mWR ≥ 18 TeV Turning this argument around, if a positive signal for WR is observed at the LHC, this will falsify leptogenesis as a mechanism for understanding the origin of matter in L-R seesaw framework.
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