S. T. Petcov

Low Energy Signatures of the TeV Scale See-Saw Mechanism

We study a type I see-saw scenario where the right-handed (RH) neutrinos, responsible for the light neutrino mass generation, lie at the electroweak scale. Under certain conditions, the strength of the charged and neutral current weak interactions of the Standard Model particles with the heavy RH neutrinos can be large enough to allow their production at the LHC, opening also the possibility of observing other low energy signatures of the new physics in the electroweak precision observables as well as in searches for rare leptonic decays or neutrinoless double beta decay. We argue that in this scenario the flavour structure of the neutrino Yukawa couplings is essentially determined by the low energy neutrino parameters, leading to fairly strong correlations among the new phenomena. In particular, we show that the present bound on the

Sizeable θ 13 from the charged lepton sector in SU(5), (tri-)bimaximal neutrino mixing and Dirac CP violation

mu to e +gamma

The μ − e conversion in nuclei, μ → eγ, μ → 3e decays and TeV scale see-saw scenarios of neutrino mass generation

decay rate makes very difficult the observation of the heavy RH neutrinos at the LHC or the observation of deviations from the Standard Model predictions in the electroweak precision data. We also argue that all present experimental constraints on this scenario still allow i) for an enhancement of the rate of neutrinoless double beta decay, which thus can be in the range of sensitivity of the GERDA experiment even when the light Majorana neutrinos possess a normal hierarchical mass spectrum, and ii) for the predicted

Majorana Phases and Leptogenesis in See-Saw Models with A 4 Symmetry

mu to e+ gamma

Predicting the values of the leptonic CP violation phases in theories with discrete flavour symmetries

decay rate to be within the sensitivity range of the MEG experiment.

Determining the Dirac CP Violation Phase in the Neutrino Mixing Matrix from Sum Rules

The recent results from T2K and MINOS experiments point towards a relatively large value of the reactor angle θ13 in the lepton sector. In this paper we show how a large θ13 can arise from the charged lepton sector alone in the context of an SU(5) GUT. In such a scenario (tri-)bimaximal mixing in the neutrino sector is still a viable possibility. We also analyse the general implications of the considered scenario for the searches of CP violation in neutrino oscillations.

Nonzero |Ue3| from charged lepton corrections and the atmospheric neutrino mixing angle

A bstractWe perform a detailed analysis of lepton flavour violation (LFV) within minimal see-saw type extensions of the Standard Model (SM), which give a viable mechanism of neutrino mass generation and provide new particle content at the electroweak scale. We focus, mainly, on predictions and constraints set on each scenario from μ → eγ, μ → 3e and μ − e conversion in the nuclei. In this class of models, the flavour structure of the Yukawa couplings between the additional scalar and fermion representations and the SM leptons is highly constrained by neutrino oscillation measurements. In particular, we show that in some regions of the parameters space of type I and type II see-saw models, the Dirac and Majorana phases of the neutrino mixing matrix, the ordering and hierarchy of the active neutrino mass spectrum as well as the value of the reactor mixing angle θ13 may considerably affect the size of the LFV observables. The interplay of the latter clearly allows to discriminate among the different low energy see-saw possibilities.

A supersymmetricSU(5)×T′unified model of flavor with largeθ13

The related issues of Majorana CP violation in the lepton sector and lepto- genesis are investigated in detail in two rather generic supersymmetric models with type I see-saw mechanism of neutrino mass generation and A4 a vour symmetry, which naturally lead at leading order to tri-bimaximal neutrino mixing. The neutrino sector in this class of models is described at leading order by just two real parameters and one phase. This leads, in particular, to signican t low energy constraints on the Majorana phases 21 and 31 in the PMNS matrix, which play the role of leptogenesis CP violating parameters in the generation of the baryon asymmetry of the Universe. We nd that it is possible to generate the correct size and sign of the baryon asymmetry in both A4 models. The sign of the baryon asymmetry is directly related to the signs of sin 21 and/or sin 31.

Higgs decays in the low scale type I see-saw model

Using the fact that the neutrino mixing matrix U=Ue†Uν, where Ue and Uν result from the diagonalisation of the charged lepton and neutrino mass matrices, we consider a number of forms of Uν associated with a variety of discrete symmetries: i) bimaximal (BM) and ii) tri-bimaximal (TBM) forms, the forms corresponding iii) to the conservation of the lepton charge L′=Le−Lμ−Lτ (LC), iv) to golden ratio type A (GRA) mixing, v) to golden ratio type B (GRB) mixing, and vi) to hexagonal (HG) mixing. Employing the minimal form of Ue, in terms of angles and phases it contains, that can provide the requisite corrections to Uν so that reactor, atmospheric and solar neutrino mixing angles θ13, θ23 and θ12 have values compatible with the current data, including a possible sizable deviation of θ23 from π/4, we discuss the possibility to obtain predictions for the CP violation phases in the neutrino mixing matrix. Considering the “standard ordering” of the 12 and the 23 rotations in Ue and following the approach developed in [1] we derive predictions for the Dirac phase δ and the rephasing invariant JCP in the cases of GRA, GRB and HG forms of Uν (results for the TBM and BM (LC) forms were obtained in [1]). We show also that under rather general conditions within the scheme considered the values of the Majorana phases in the PMNS matrix can be predicted for each of the forms of Uν discussed. We give examples of these predictions and of their implications for neutrinoless double beta decay. In the GRA, GRB and HG cases, as in the TBM one, relatively large CP violation effects in neutrino oscillations are predicted (|JCP|∼(0.031–0.034)). Distinguishing between the TBM, BM (LC), GRA, GRB and HG forms of Uν requires a measurement of cosu2061δ or a relatively high precision measurement of JCP.

Multiple CP non-conserving mechanisms of (ββ)0ν -decay and nuclei with largely different nuclear matrix elements

Abstract Using the fact that the neutrino mixing matrix U = U e † U ν , where U e and U ν result from the diagonalisation of the charged lepton and neutrino mass matrices, we analyse the sum rules which the Dirac phase δ present in U satisfies when U ν has a form dictated by, or associated with, discrete symmetries and U e has a “minimal” form (in terms of angles and phases it contains) that can provide the requisite corrections to U ν , so that reactor, atmospheric and solar neutrino mixing angles θ 13 , θ 23 and θ 12 have values compatible with the current data. The following symmetry forms are considered: i) tri-bimaximal (TBM), ii) bimaximal (BM) (or corresponding to the conservation of the lepton charge L ′ = L e − L μ − L τ (LC)), iii) golden ratio type A (GRA), iv) golden ratio type B (GRB), and v) hexagonal (HG). We investigate the predictions for δ in the cases of TBM, BM (LC), GRA, GRB and HG forms using the exact and the leading order sum rules for cos u2061 δ proposed in the literature, taking into account also the uncertainties in the measured values of sin 2 u2061 θ 12 , sin 2 u2061 θ 23 and sin 2 u2061 θ 13 . This allows us, in particular, to assess the accuracy of the predictions for cos u2061 δ based on the leading order sum rules and its dependence on the values of the indicated neutrino mixing parameters when the latter are varied in their respective 3σ experimentally allowed ranges.