Neutrino masses and mixing with non-anomalous abelian flavor symmetries

Nir, Yosef; Shadmi, Yael

doi:10.1088/1126-6708/1999/05/023

Cited by 25 publications

(11 citation statements)

References 41 publications

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“…Equal VEVs S L = SL would be necessary to preserve supersymmetry with a gauged, non-anomalous U (1) L . Similarly, two spurions of equal VEVs and opposite U (1) H charges would be necessary if U (1) H is a gauged, non-anomalous symmetry [9]. Neither ingredient is important for our purposes.…”

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confidence: 99%

The Importance of Being Majorana: Neutrinos versus Charged Fermions in Flavor Models

Nir

Shadmi

2004

J. High Energy Phys.

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We argue that neutrino flavor parameters may exhibit features that are very different from those of quarks and charged leptons. Specifically, within the Froggatt-Nielsen (FN) framework, charged fermion parameters depend on the ratio between two scales, while for neutrinos a third scale-that of lepton number breaking-is involved. Consequently, the selection rules for neutrinos may be different. In particular, if the scale of lepton number breaking is similar to the scale of horizontal symmetry breaking, neutrinos may become flavor-blind even if they carry different horizontal charges. This provides an attractive mechanism for neutrino flavor anarchy.Introduction. The measured neutrino flavor parameters are neither manifestly small (apart from the overall mass scale) nor manifestly hierarchical. The two measured mixing angles are O(1) and the measured mass ratio is O(0.2) or larger. With the upper bound on the third mixing angle of O(0.2), and with no information on the remaining mass ratio and CP violating phases, it could well be that all neutrino flavor parameters are nonhierarchical, that is, anarchical [1] (see however [2]). This is in sharp contrast to the charged fermion flavor parameters. Of these, only two parameters-the top Yukawa and the KM phase-are O(1), while all other eleven parameters-eight masses and three mixing angles-are small and hierarchical.It is of course possible that yet-unmeasured neutrino parameters (θ 13 and/or m 1 /m 2 ) are small, and there is hierarchy in all sectors. We assume here that this is not the case. Then, it is interesting to understand the reason for the difference between the flavor structure of neutral and charged fermions. This difference could be accidental. For example, one could imagine that the flavor structure is a result of an approximate symmetry, and it just so happens that all lepton doublets carry the same charge under this symmetry (see, for example, [3]). In other words, each of the sectors-up, down, charged lepton and neutrino-could equally well be hierarchical or accidentally anarchical. However, a far more intriguing possibility is that the difference is due to the fact that, of all the standard model fermions, only neutrinos are Majorana fermions. Then the measured parameters reflect the interplay between flavor physics and lepton number violation. It is this interplay that we wish to explore.In order to relate the flavor structure and the Majorana/Dirac nature of fermions, one must work within a framework that explains the flavor hierarchy of quarks and charged leptons. One of the most attractive such frameworks is the Froggatt-Nielsen (FN) mechanism [4]. One assumes an Abelian horizontal symmetry that is broken by a small parameter near some high "flavor scale", M F . This implies various selection rules for the flavor

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The Importance of Being Majorana: Neutrinos versus Charged Fermions in Flavor Models

Nir

Shadmi

2004

J. High Energy Phys.

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“…In Ref. [16] it was argued, however, that in Abelian flavor models that satisfy both (1.1) and (1.2), the pseudo-Dirac structure cannot apply to the 23 subspace. It can only be relevant then to the 12 subspace, corresponding to either the MSW(LA) or the VO solution of the SN problem.…”

Section: Pseudo-dirac Neutrinosmentioning

confidence: 99%

“…(In Ref. [16], these models are called (2,0) models, where the first integer refers to the number of active neutrinos, and the second to the number of sterile.) In such models, the selection rules apply directly to the Majorana mass matrix of the active neutrinos, and it is easy to see that the neutrino mass matrix cannot give both large mixing and hierarchically separated masses: Large 23 mixing would require (M ν ) 23 ∼ (M ν ) 33 .…”

Section: Avoidingmentioning

confidence: 99%

“…(1.2) have been constructed in Ref. [16]. In the models of [16], the large mixing in the 23 subspace is achieved by…”

Section: Two Breaking Parametersmentioning

confidence: 99%

“…Our work is closely related to that of Refs. [15,16] where the various classes of models of Abelian flavor symmetries that can accommodate (1.1) and (1.2) were presented. Here we analyze the consequences of these classes of models for charged LFV.…”

Section: Introductionmentioning

confidence: 99%

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Neutrino parameters, Abelian flavor symmetries, and charged lepton flavor violation

Feng

Nir²,

Shadmi³

2000

Phys. Rev. D

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Neutrino masses and mixings have important implications for models of fermion masses, and, most directly, for the charged lepton sector. We consider supersymmetric Abelian flavor models, where neutrino mass parameters are related to those of charged leptons and sleptons. We show that processes such as τ → µγ, µ → eγ and µ − e conversion provide interesting probes. In particular, some existing models are excluded by current bounds, while many others predict rates within reach of proposed near future experiments. We also construct models in which the predicted rates for charged lepton flavor violation are below even the proposed experimental sensitivities, but argue that such models necessarily involve loss of predictive power. 11/991 On leave of absence from Princeton University.

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Contributed report: Flavor anarchy for Majorana neutrinos

Nir

Shadmi

2004

Pramana - J Phys

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Neutrino masses and mixing with non-anomalous abelian flavor symmetries

Cited by 25 publications

References 41 publications

The Importance of Being Majorana: Neutrinos versus Charged Fermions in Flavor Models

The Importance of Being Majorana: Neutrinos versus Charged Fermions in Flavor Models

Neutrino parameters, Abelian flavor symmetries, and charged lepton flavor violation

Contributed report: Flavor anarchy for Majorana neutrinos

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