Abstract
We explore the possibility of having a successful leptogenesis through oscillations between new sterile fermion states added to the Standard Model field content in a well motivated framework, naturally giving rise to the required mass splitting between the sterile states through a small total lepton number violation. We propose a framework with only two sterile states forming a pseudo-Dirac state, in which their mass difference as well as the smallness of the neutrino masses are due to two sources of lepton number violation with Δ L=2, corresponding to an Inverse Seesaw framework extended by a Linear Seesaw mass term. We also explore the pure Inverse Seesaw mechanism in its minimal version, requiring at least four new sterile states in order to comply with neutrino data. Our analytical and numerical studies reveal that one can have a successful leptogenesis at the temperature of the electroweak scale through oscillations between the two sterile states with a ``natural'' origin of the strong degeneracy in their mass spectrum. We also revisit the analytical expression of the baryon asymmetry of the Universe in the weak washout regime of this framework.
Highlights
The origin of neutrino masses and the leptonic mixing, the Dark Matter (DM) nature and the origin of the baryon asymmetry of the Universe (BAU) are three of the most pressing open questions of particle and astroparticle physics.In order to account for neutrino masses and mixings, many extensions of the Standard Model (SM) call upon the introduction of right-handed neutrinos - which are sterile states - giving rise to a Dirac mass term for the neutral leptons
In this work we have proposed a minimal extension of the Standard Model by adding two sterile fermions with opposite lepton number, forming a setup with an approximate lepton number conservation
The small mass splitting within this pair, as well as the smallness of the active neutrino masses, are due to two sources of lepton number violation with ∆L = 2, corresponding to an Inverse Seesaw framework extended by a Linear Seesaw mass term
Summary
The origin of neutrino masses and the leptonic mixing, the Dark Matter (DM) nature and the origin of the baryon asymmetry of the Universe (BAU) are three of the most pressing open questions of particle and astroparticle physics. The degeneracy between the heavy neutrinos, which is phenomenologically imposed in the νMSM, can be naturally explained in frameworks in which the smallness of (active) neutrino masses is directly linked to a small violation of the total lepton number [27] This can be achieved when, for instance, the Inverse Seesaw [6, 28] mechanism is embedded into the SM. The present study focuses on the possibility of simultaneously having a very low scale seesaw mechanism - typically at 1 − 10 GeV - at work for generating neutrino masses and mixings as well as an efficient leptogenesis at the electroweak scale, by considering a “natural” and minimal framework (with only two additional neutrinos) giving rise to the needed degeneracy in the spectrum of the sterile states. We provide in Appendix B the relevant numerical input parameters for all the solutions discussed in this work
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