Lepton number violation as a key to low-scale leptogenesis

Abstract

We explore the possibility of having a successful leptogenesis through\noscillations between new sterile fermion states added to the Standard Model\nfield content in a well motivated framework, naturally giving rise to the\nrequired mass splitting between the sterile states through a small total lepton\nnumber violation. We propose a framework with only two sterile states forming a\npseudo-Dirac state, in which their mass difference as well as the smallness of\nthe neutrino masses are due to two sources of lepton number violation with\n$\\Delta L=2$, corresponding to an Inverse Seesaw framework extended by a Linear\nSeesaw mass term. We also explore the pure Inverse Seesaw mechanism in its\nminimal version, requiring at least four new sterile states in order to comply\nwith neutrino data. Our analytical and numerical studies reveal that one can\nhave a successful leptogenesis at the temperature of the electroweak scale\nthrough oscillations between the two sterile states with a "natural" origin of\nthe strong degeneracy in their mass spectrum. We also revisit the analytical\nexpression of the baryon asymmetry of the Universe in the weak washout regime\nof this framework.\n