Abstract
We make a comparative study of the neutrinoless double beta decay constraints on heavy sterile neutrinos versus other direct and indirect constraints from both lepton number conserving and violating processes, as a sensitive probe of the extent of lepton number violation and possible interference effects in the sterile sector. We introduce a phenomenological parametrisation of the simplified one-generation seesaw model with one active and two sterile neutrino states in terms of experimentally measurable quantities, such as active-sterile neutrino mixing angles, CP phases, masses and mass splittings. This simple parametrisation enables us to analytically derive a spectrum of possible scenarios between the canonical seesaw with purely Majorana heavy neutrinos and inverse seesaw with pseudo-Dirac ones. We then go on to constrain the simplified parameters of this model from various experiments at the energy, intensity and cosmic frontiers. We emphasise that the constraints from lepton number violating processes strongly depend on the mass splitting between the two sterile states and the relative CP phase between them. This is particularly relevant for neutrinoless double beta decay, which is weakened for small mass splitting and opposite CP parities between the sterile states. On the other hand, neutrinoless double beta decay is especially sensitive for Majorana sterile neutrinos with masses around 0.1 − 10 GeV.
Highlights
Principle generate a Dirac mass term; to get sub-eV left-handed (LH) neutrino masses as required by the neutrino oscillation data, one needs the Dirac Yukawa couplings to be 10−12
We introduce a phenomenological parametrisation of the simplified one-generation seesaw model with one active and two sterile neutrino states in terms of experimentally measurable quantities, such as active-sterile neutrino mixing angles, CP phases, masses and mass splittings
In order to put the neutrinoless double beta (0νββ) decay sensitivity into context, we review the experimental constraints on the sterile neutrino sector from both lepton number conserving (LNC) and violating channels from high-energy collider searches, high-intensity beam dump and meson decay experiments, beta decays and other nuclear processes, activesterile neutrino oscillation experiments, electroweak precision data and other indirect laboratory searches, as well as cosmological and astrophysical observations
Summary
We consider the addition of two SM-singlet Weyl fermions νR, and νR, to the SM particle content. Only one sterile state is minimally required to give mass to the one active neutrino considered here, i.e. The minimal inverse seesaw [25,26,27] incorporates (MD)2 = 0 and (MS)11 = 0, so the neutrino mass matrix (2.2) becomes. Whether any one of the terms in eq (2.2) violates lepton number will depend on the L assignment for the two sterile neutrinos νR,, νR,2. The smallness of the parameters μR,S,F in the three seesaw variants discussed above is technically natural in the ’t Hooft sense [43], i.e. in the limit of μR,S,F → 0, lepton number symmetry is restored and the light neutrino νL,e is exactly massless to all orders in perturbation theory, as in the SM
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
