Neutrinoless double beta decay in seesaw models

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.

Section: Constraintsmentioning

confidence: 86%

Electron electric dipole moment in Inverse Seesaw models

Abada

Toma

2016

“…However, the price to obtain measurable flavour-changing rates with hierarchical spectra is to induce unacceptably large neutrino masses, disregarding eventual large fine-tuning between the various parameters 4 (which anyway would be destabilized by unacceptably large radiative contributions to neutrino masses [46]). Moreover, the heavy right-handed neutrino contribution to neutrinoless double beta decay can be in contradiction with the current bound [47][48][49], especially for low righthanded neutrino masses below a few tens of GeV. In consequence, in the rest of the paper we will consider only the quasi-degenerate spectrum of right-handed neutrinos.…”

Section: Phenomenological Frameworkmentioning

confidence: 89%

Muon conversion to electron in nuclei in type-I seesaw models

Alonso

Dhen

Gavela

et al. 2013

171

175

We compute the µ → e conversion in the type-I seesaw model, as a function of the right-handed neutrino mixings and masses. The results are compared with previous computations in the literature. We determine the definite predictions resulting for the ratios between the µ → e conversion rate for a given nucleus and the rate of two other processes which also involve a µ − e flavour transition: µ → eγ and µ → eee. For a quasi-degenerate mass spectrum of right-handed neutrino masses -which is the most natural scenario leading to observable rates-those ratios depend only on the seesaw mass scale, offering a quite interesting testing ground. In the case of sterile neutrinos heavier than the electroweak scale, these ratios vanish typically for a mass scale of order a few TeV. Furthermore, the analysis performed here is also valid down to very light masses. It turns out that planned µ → e conversion experiments would be sensitive to masses as low as 2 MeV. Taking into account other experimental constraints, we show that future µ → e conversion experiments will be fully relevant to detect or constrain sterile neutrino scenarios in the 2 GeV−1000 TeV mass range.

“…In our analysis, we evaluate the contributions of the sterile states to the effective mass m ee according to [66,67]; strong bounds on the effective mass have been set by several experiments, among them GERDA [68], EXO-200 [69,70], KamLAND-ZEN [71]. In our analysis we use the most recent constraint from [70].…”

Section: Jhep02(2016)083mentioning

confidence: 99%

Impact of sterile neutrinos on nuclear-assisted cLFV processes

Abada

Romeri

Teixeira

2016

We discuss charged lepton flavour violating processes occurring in the presence of muonic atoms, such as muon-electron conversion in nuclei CR(µ − e, N), the (Coulomb enhanced) decay of muonic atoms into a pair of electrons BR(µ − e − → e − e − , N), as well as Muonium conversion and decay, Mu − Mu and Mu → e + e − . Any experimental signal of these observables calls for scenarios of physics beyond the Standard Model. In this work, we consider minimal extensions of the Standard Model via the addition of sterile fermions, providing the corresponding complete analytical expressions for all the considered observables. We first consider an "ad hoc" extension with a single sterile fermion state, and investigate its impact on the above observables. Two well motivated mechanisms of neutrino mass generation are then considered: the Inverse Seesaw embedded into the Standard Model, and the νMSM. Our study reveals that, depending on their mass range and on the active-sterile mixing angles, sterile neutrinos can give significant contributions to the above mentioned observables, some of them even lying within present and future sensitivity of dedicated cLFV experiments. We complete the analysis by confronting our results to other (direct and indirect) searches for sterile fermions.