Search for Neutrinoless Double-Beta Decay in Xe 136 with EXO-200

We propose a complex extension of µτ permutation antisymmetry in the neutrino Majorana matrix M ν . The latter can be realized for the Lagrangian by appropriate CP transformations on the neutrino fields. The resultant form of M ν is shown to be simply related to that with a complex (CP) extension of µτ permutation symmetry, with identical phenomenological consequences, though their group theoretic origins are quite different. We investigate those consequences in detail for the minimal seesaw induced by two strongly hierarchical right-chiral neutrinos N 1 and N 2 with the result that the Dirac phase is maximal while the two Majorana phases are either 0 or π. We further provide an uptodate discussion of the ββ0ν process vis-a-vis ongoing and forthcoming experiments. Finally, a thorough treatment is given of baryogenesis via leptogenesis in this scenario, primarily with the assumption that the lepton asymmetry produced by the decays of N 1 only matters here with the asymmetry produced by N 2 being washed out. Tight upper and lower bounds on the mass of N 1 are obtained from the constraint of obtaining the correct observed range of the baryon asymmetry parameter and the role played by N 2 is elucidated thereafter. The mildly hierarchical right-chiral neutrino case (including the quasidegenerate possibility) is discussed in an appendix.

“…KamLAND-Zen [74] and EXO [75] had earlier constrained this value to be < 0.35 eV. But the most impressive upper bound till date is provided by GERDA phase-II data [76]: M ee < 0.098 eV.…”

Section: Jhep06(2018)085mentioning

confidence: 99%

Consequences of minimal seesaw with complex μτ antisymmetry of neutrinos

Samanta

Roy

Ghosal

2018

“…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.

“…Blue and red regions represent predictions for normal and inverted hierarchy for the value n = 8 (in the top-right panel, we choose n = 5 which is the smallest viable value of n in that case). The upper bound |m ee | < 0.120 eV is given by measurements by the EXO-200 [72,73] and KamLAND-ZEN experiments [74]. Planck data in combination with other CMB and BAO measurements [75] provides a limit on the sum of neutrino masses of m 1 + m 2 + m 3 < 0.230 eV from which the upper limit on the mass of the lightest neutrino can be derived.…”

Section: Jhep12(2014)007mentioning

confidence: 99%

Generalised CP and Δ(6n 2) family symmetry in semi-direct models of leptons

Ding

King

Neder

2014

Abstract:We perform a detailed analysis of ∆(6n 2 ) family symmetry combined with a generalised CP symmetry in the lepton sector, breaking to different remnant symmetries G ν in the neutrino and G l in the charged lepton sector, together with different remnant CP symmetries in each sector. We discuss the resulting mass and mixing predictions for G ν = Z 2 with G l = K 4 , Z p , p > 2 and G ν = K 4 with G l = Z 2 . All cases correspond to the preserved symmetry smaller than the full Klein symmetry, as in the semi-direct approach, leading to predictions which depend on a single undetermined real parameter, which mainly determines the reactor angle. We focus on five phenomenologically allowed cases for which we present the resulting predictions for the PMNS parameters as a function of n, as well as the predictions for neutrinoless double beta decay.