Abstract
We consider the contribution of sterile neutrinos to the electric dipole moment of charged leptons in the most minimal realisation of the Inverse Seesaw mechanism, in which the Standard Model is extended by two right-handed neutrinos and two sterile fermion states. Our study shows that the two pairs of (heavy) pseudo-Dirac mass eigenstates can give significant contributions to the electron electric dipole moment, lying close to future experimental sensitivity if their masses are above the electroweak scale. The major contribution comes from two-loop diagrams with pseudo-Dirac neutrino states running in the loops. In our analysis we further discuss the possibility of having a successful leptogenesis in this framework, compatible with a large electron electric dipole moment.
Highlights
Some of the latter scenarios may provide a possible explanation to the dark matter relic density considering, putting forward a keV-scale sterile neutrino as a viable candidate [11, 17], and/or to the BAU through leptogenesis [18,19,20,21,22,23]
Our study shows that the two pairs of pseudo-Dirac mass eigenstates can give significant contributions to the electron electric dipole moment, lying close to future experimental sensitivity if their masses are above the electroweak scale
In a recent work [47], we studied the impact of sterile fermions on the electric dipole moments of charged leptons in the context of the SM extended by an arbitrary number1 of sterile neutrinos — without necessarily invoking a mechanism of neutrino mass generation — and we have shown that in order to have a non-vanishing contribution, the minimal number of sterile fermion states that must be added to the SM field content is two
Summary
As argued in [14], the minimal realisation of the Inverse Seesaw model requires the addition of two right-handed neutrinos Ni, and two singlet fermions si to the SM field content. Assigning the same lepton numbers (L = +1) to Ni and si allows for a small ∆L = 2 lepton number violating (LNV) mass parameter μ and m, corresponding to Majorana masses in the sterile sector This leads to the following neutrino mass terms in the Lagrangian. We will neglect the mass parameters mij, which induce subdominant effects when compared to the entries μij in the mass matrix of eq (2.3) Both these lepton number violating mass matrices can be dynamically generated as done in the general original formulation of the Inverse Seesaw mechanism [8], in which the smallness of the μ matrix elements was attributed to supersymmetry breaking effects in a (superstring inspired) E6 scenario.
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