In this paper, we consider a neutrino mass model based on $A_4$ symmetry. The spontaneous symmetry breaking in this model is chosen to obtain tribimaximal mixing in the neutrino sector. We introduce $Z_2 \times Z_2$ invariant perturbations in this model which can give rise to acceptable values of $θ_{13}$ and $δ_{CP}$. Perturbation in the charged lepton sector alone can lead to viable values of $θ_{13}$, but cannot generate $δ_{CP}$. Perturbation in the neutrino sector alone can lead to acceptable $θ_{13}$ and maximal CP violation. By adjusting the magnitudes of perturbations in both sectors, it is possible to obtain any value of $δ_{CP}$.
It is proposed that light neutrinos form a triplet in a global SU(3) flavor symmetry. Within this framework, a symmetry principle predicts sin^2 theta_{23}=0.5 and gives the so called inverted neutrino mass hierarchy, theta _{13}=0 and a small deviation from pi/4 for theta_{12}.
I consider parity violation of the chiral symmetry broken vacuum. It is shown that the parity of the true vacuum in the chiral symmetry breaking model is violated. I propose new mechanism of massive neutrino, which the neutrinos have mass in terms of the chiral symmetry breaking. In this mechanism, it may give us new understanding why almost neutrinos have left chirality. Further, NJL model is proposed as alternative phenomenological model of neutrinos.
Neutrino flavor conversion is assumed to be induced by right-handed neutrino flavor conversion via seesaw mechanism. Neutrino oscillation is the macroscopic phenomenon before all neutrino flavor-flip interactions reaching equilibrium. The model for the hypothesis is the extension by introducing large mass Majorana right-handed neutrino into the Standard Model and exerting horizontal symmetry only on the right-handed neutrino sector.
We demonstrate that an $SU(2)_L\times U(1)_Y$ model with extended Higgs sector gives rise to bi-maximal neutrino mixing through the incorporation of SO(3) flavour symmetry and discrete symmetry. The neutrino and the charged lepton masses are generated due to higher dimensional terms. The hierarchical structures of neutrinos and charged leptons are obtained due to inclusion of SO(3) flavour symmetry and discrete symmetry.The model can accommodate the vacuum oscillation solution of solar neutrino problem, through reasonable choice of model parameters along with the atmospheric neutrino experimen…
The permutation symmetry $S_3$ is appplied to obtain two equal Majorana neutrino masses, while maintaining three different charged-lepton masses and suppressing neutrinoless double beta decay. The resulting radiative splitting of the two neutrinos is shown to be suitable for solar neutrino vacuum oscillations.
The problem of generating large transition magnetic moments for nearly massless neutrinos in a truly three--generation case is discussed. A model to achieve the same by exploiting an octahedral symmetry is presented. The scheme also accomodates a radiatively generated mass of $17\:keV$ for a pseudo--Dirac neutrino that decays rapidly through the Majoron channel.
The vacuum neutrino mixing is known to exhibit an approximate $μ-τ$ symmetry, which was shown to be preserved for neutrino propagating in matter. This symmetry reduces the neutrino transition probabilities to very simple forms when expressed in a rephasing invariant parametrization introduced earlier. Applications to long baseline experiments are discussed.
We write out the generic Dirac neutrino mass operator which possesses the Friedberg-Lee (FL) symmetry and find that its corresponding neutrino mass matrix is asymmetric. Following a simple way to break the FL symmetry, we calculate the neutrino mass eigenvalues and show that the resultant neutrino mixing pattern is nearly tri-bimaximal. Imposing the Hermitian condition on the neutrino mass matrix, we also show that the simplified ansatz is consistent with current experimental data and favors the normal neutrino mass hierarchy.
We have studied the large mixing angle MSW solution for the solar neutrinos in the non-abelian flavor symmetry. We predict the MNS mixing matrix taking account of the symmetry breakings.
Many studies have been made on extensions of the standard model with $B-L$ gauge symmetry. The addition of three singlet (right-handed) neutrinos renders it anomaly-free. It has always been assumed that the spontaneous breaking of $B-L$ is accomplished by a singlet scalar field carrying two units of $B-L$ charge. This results in a very natural implementation of the Majorana seesaw mechanism for neutrinos. However, there exists in fact another simple anomaly-free solution which allows Dirac or inverse seesaw neutrino masses. We show for the first time these new possibilities and discuss an appl…
In a model with four neutrino mass eigenstates grouping in two narrow doublets the condition of maximal mixing of the doublet neutrino components leads to a simple four-neutrino mixing matrix which is related to two connected effective two-neutrino mixing patterns. As a result, large values of the neutrino oscillation amplitudes for both the solar and atmospheric neutrino anomalies appear quite naturally if the LSND data are accepted.
We examine a recently proposed symmetry/condition by Friedberg and Lee in the framework where three right-handed neutrinos are added to the spectrum of the three-family Minimal Standard Model. It is found that the right-handed neutrinos are very special, with respect to this symmetry. In the symmetry limit the neutrinos are massless and that may be a hint about why they are light. Imposed as a condition and not as a full symmetry, we find that one of the three right-handed neutrinos simply decouples (has only gravitational interactions) and that there is a massless interacting neutrino. The po…
It is shown how a mechanism which allows naturally small Dirac neutrino masses is linked to the existence of dark matter through an anomaly-free U(1) gauge symmetry of fermion singlets.
A $Z_{2L}\times Z_{2R}$ generation symmetry in the neutrino sector predicts the atmospheric neutrino mixing to be maximal, and the MNS matrix element $U_{e3}$ to be zero, consistent with observations. Solar neutrino mixing may be maximal but is not required by the symmetry. Neutrino masses of the first two generations are predicted to vanish, providing a first approximation to the oscillation data. The consequence of a smaller $Z_2$ symmetry is also discussed. In that case, deviation from the $Z_{2L}\times Z_{2R}$ result is of the order of the neutrino mass ratio between the first two generati…
We propose a flavour theory of leptons implementing an $A_4$ family symmetry. Our scheme provides a simple way to derive trimaximal neutrino mixing from first principles, leading to simple and testable predictions for neutrino mixing and CP violation. Dark matter mediates neutrino mass generation, as in the simplest scotogenic model.
Assuming hierarchical neutrino masses we calculate the heavy neutrino mass scale in the seesaw mechanism from experimental data on oscillations of solar and atmospheric neutrinos and quark-lepton symmetry. The resulting scale is around or above the unification scale, unless the two lightest neutrinos have masses of opposite sign, in which case the resulting scale can be intermediate.
A new mechanism is proposed to explain neutrino masses and their mixing via SU(1,1) horizontal symmetry breaking. Based on this mechanism smallness of neutrino masses is naturally realized and inverted hierarchical spectrum with large mixing is given.
Predictive spontaneous CP violation is possible if it is obtained geometrically through a non-Abelian discrete symmetry. I propose such a model of neutrino mass and mixing based on Delta(27).
The toy fermion model coupled with Lagrange multiplier constraint field is proposed. The possibility of superluminal neutrino propagation as result of dynamical Lorentz symmetry breaking is studied.
The current searches for neutrino oscillations seem to suggest an approximate $L_e-L_\m-L_τ$ flavor symmetry. This symmetry implies a pair of degenerate neutrinos with mass $m_0$ and large leptonic mixing. We explore the possibility that gravitational interactions break this global symmetry. The Planck scale suppressed breaking of the $L_e-L_\m-L_τ$ symmetry is shown to lead to the right amount of splitting among the degenerate neutrinos needed in order to solve the solar neutrino problem. The common mass $m_0$ of the pair can be identified with the atmospheric neutrino scale. A concrete model…
The three neutrino mass matrices in the $SU(5)\times U(2)$ model are studied focusing on the neutrino oscillation experiments. The atmospheric neutrino anomaly could be explained by the large $ν_μ - ν_τ$ oscillation. The long baseline experiments are expected to detect signatures of the neutrino oscillation even if the atmospheric neutrino anomaly is not due to the neutrino oscillation. However, the model cannot solve the solar neutrino deficit while it could be reconciled with the LSND data.
Assuming that the neutrino mass matrix is dominated by a term with the permutation symmetry $S_{\scriptscriptstyle 3}$ it is possible to explain neutrino data only if the masses are quasi-degenerate. A sub-dominant term with an approximate $μ-τ$ symmetry leads to an approximate tri-bimaximal form. Experimental consequences are discussed.
We propose a neutrino model in which neutrino masses are generated at one loop level and three right-handed fermions have non-trivial charges under $U(1)_{B-L}$ gauge symmetry in no conflict with anomaly cancellation. After the spontaneously symmetry breaking, a remnant $Z_2$ symmetry is induced and plays an role in assuring the stability of dark matter candidate.
We consider an Supersymmetric extension of the Standard Model with some extra Higgs doublets and a global $(B - L)$, where $B$ and $L$ are the usual baryonic and lepton number respectivelly, and ${\cal Z}_{3} \otimes {\cal Z}^{\prime}_{3}$ symmetries of the non-SUSY model presented at [1]..
In a new application of the discrete non-Abelian symmetry A_4 using the canonical seesaw mechanism, a three-parameter form of the neutrino mass matrix is derived. It predicts the following mixing angles for neutrino oscillations: theta_{13}=0, sin^2 theta_{23}=1/2, and sin^2 theta_{12} close, but not exactly equal to 1/3, in one natural symmetry limit.
The scotogenic model of radiative neutrino mass with $Z_2$ or $U(1)_D$ dark matter is shown to accommodate $Δ(27)$ symmetry naturally. The resulting neutrino mass matrix is identical to either of two forms, one proposed in 2006, the other in 2008. These two structures are studied in the context of present neutrino data, with predictions of $CP$ violation and neutrinoless double beta decay.
Neutrino oscillation data indicate the presence of a 2-3 symmetry for the left-handed neutrinos. We show that this symmetry between the second and third generations cannot be extended to include the charged leptons, no matter what basis we use. We point out that if this symmetry is also independently valid for the right-handed neutrinos, then the active neutrino spectrum is inverted, with $m_3=0$. This conclusion remains valid even when the left-handed 2-3 symmetry is broken by a non-maximal atmospheric mixing angle $θ_{23}$, or a non-zero reactor angle $θ_{13}$. As previously shown by Mohapat…
Maximum mixing in atmospheric neutrino oscillation, as well as vanishing of the MNS matrix element $U_{e3}$, are consequences of a 2-3 symmetry, under which the neutrino mass matrix is invariant under the interchange of second and third generation neutrinos. These predictions of the 2-3 symmetry are consistent with the results of Super-Kamiokande, K2K, and CHOOZ experiments. If the symmetry is exact at a high-energy scale set by right-handed neutrinos, a deviation from these predictions generated by renormalization-group corrections will occur at experimental energies. With an MSSM dynamics, t…
Continuous $U(1)_{L_μ-L_τ}$ symmetry can generate quasi degenerate mass spectrum for both left handed light and right handed heavy Majorana neutrinos assuming that the symmetry preserving non zero parameters are nearly same. There is an accidental $μτ$ exchange symmetry in the light and heavy neutrino Majorana mass terms. This implies $θ_{13}=0$ and $θ_{23}=\fracπ{4}$. In addition it generates another zero mixing angle and one zero mass difference. We restrict ourselves to type-I See-Saw mechanism for generation of light neutrino mass. We have found that under $U(1)_{L_μ-L_τ}$ symmetry cosmolo…
We propose a model which is a simple extension of the KSVZ invisible axion model with an inert doublet scalar. Peccei-Quinn symmetry forbids tree-level neutrino mass generation and its remnant $Z_2$ symmetry guarantees dark matter stability. The neutrino masses are generated by one-loop effects as a result of the breaking of Peccei-Quinn symmetry through a nonrenormalizable interaction. Although the low energy effective model coincides with an original scotogenic model which contains right-handed neutrinos with large masses, it is free from the strong $CP$ problem.
We consider nucleosynthesis constraints on models which use chiral symmetry breaking as a basis for understanding very small Dirac neutrino masses. We show that present big-bang nucleosynthesis constraints impose a well-defined upper bound of 0.1eV on the neutrino masses. This bound may become several orders of magnitude more stringent in the future as our understanding of the observational constraints on nucleosynthesis improves. We discuss the phenomenological implications for neutrino dark matter, the solar neutrino problem and the atmospheric neutrino deficit.
We present a model where Majorana neutrino mass terms are forbidden by the flavor symmetry group Delta(27). Neutrinos are Dirac fermions and their masses arise in the same way as that of the charged fermions, due to very small Yukawa couplings. The model fits current neutrino oscillation data and correlates the octant of the atmospheric angle with the magnitude of the lightest neutrino mass, with maximal mixing excluded for any neutrino mass
We argue that in order to provide a natural explanation of both neutrino mass hierarchies and large neutrino mixing angles, as required by the atmospheric neutrino data, a single right-handed neutrino must give the dominant contribution to the 23 block of the light effective neutrino matrix, and illustrate this mechanism in the framework of models with U(1) family symmetries. Sub-dominant contributions from other right-handed neutrinos are required to give small mass splittings appropriate to the small angle MSW solution to the solar neutrino problem. We give general conditions for achieving t…
We present neutrino mass matrices which predict the atmospheric neutrino mixing to be almost maximal, $\sin^2 2θ_{atm}>0.999$, as well as the large solar neutrino mixing, $8/9>\sin^2 2θ_{sol}>0.87$, and the large CP violation (the CP violation phase in the standard form is maximal $δ=π/2$), based on the $Z_3$ symmetry.
Phenomenological implications of neutrino oscillations implied by recent experimental data on pattern of neutrino mass matrix are disscussed. It is shown that it is possible to have a neutrino mass matrix which shows approximate flavor symmetry; the neutrino mass differences arise from flavor violation in off-diagonal Yukawa couplings. Two modest extensions of the standard model, which can embed the resulting neutrino mass matix have also been discussed.
Abelian family symmetries provide a predictive framework for neutrino mass models. In seesaw models based on an abelian family symmetry, the structures of the Dirac and the Majorana matrices are derived from the symmetry, and the neutrino masses and mixing angles are determined by the lepton charges under the family symmetry. Such models can lead to mass degeneracies and large mixing angles as well as mass hierarchies, the squared mass difference between quasi-degenerate neutrinos being determined by the symmetry. We present two models illustrating this approach.
For a neutrino mass matrix whose texture has an approximate flavor symmetry and where one has near degenerate neutrino mass, it is shown that the tribimaximal values for atmospheric angle $\sin^{2}{θ_{23}}=1/2$ and solar angle $\sin^{2}{θ_{12}}=1/3$ can be maintained even when the reactor angle $θ_{13}\neq0$. The non zero $\sinθ_{13}$ implies approximate $ν_μ\rightarrow-ν_τ$ symmetry instead of $ν_μ\rightarrowν_τ$ symmetry.
We propose a model with radiatively induced neutrino mass at two-loop level, applying modular $A_4$ symmetry. The neutrino mass matrix is formulated where the structure of associated couplings are restricted by the symmetry. Then we show several predictions in the lepton sector, satisfying lepton flavor violations as well as neutrino oscillation data. We also discuss muon anomalous magnetic moment and briefly comment on dark matter candidate.
Based on the SO(3) gauge symmetry for three family leptons and general see-saw mechanism, we present a simple scheme that allows three nearly degenerate Majorana neutrino masses needed for hot dark matter. The vacuum structure of the spontaneous SO(3) symmetry breaking can automatically lead to a maximal CP-violating phase. Thus the current neutrino data on both the atmospheric neutrino anomaly and solar neutrino deficit can be accounted for via maximal mixings without conflict with the current data on the neutrinoless double beta decay. The model also allows rich interesting phenomena on lept…
The prediction of vanishing reactor angle was thought to be a signature of $2$-$3$ symmetry of neutrino mass matrix. But the present study addresses certain interesting facts related with $2$-$3$ symmetry which are not addressed so far. The investigation highlights that $θ_{13}=0$, corresponds to a very special case in association with $2$-$3$ symmetry and to engender a non-zero $θ_{13}$, the breakdown of $2$-$3$ symmetry is not essential.
The discrete subgroup Delta(27) of SU(3) has the interesting multiplication rule 3 X 3 = bar{3} + bar{3} + bar{3}, which is used to obtain near tribimaximal neutrino mixing. Using present neutrino oscillation data as input, this model predicts that the effective mass m_{ee} measured in neutrinoless double beta decay will be 0.14 eV.
A sterile neutrino in the $3+1$ scheme, where the sterile accounts for neutrino anomalies not explained solely by the weak active neutrinos, arises as a natural source for the breaking of the $μ-τ$ symmetry suggested by oscillation neutrino data. We explore the predictions for the Dirac CP phases in this scenario, with and without sterile neutrino decay, and show that current limits on $δ_{CP}$ suggest a normal hierarchy and a lightest neutrino scale below 0.1~eV as the most plausible explanation for that, when Majorana phases are null. Other Dirac phases turn out to be non zero as well.
Assuming the same form of all mass matrices as motivated by quark-lepton symmetry, we discuss conditions under which bi-large mixing in the lepton sector can be obtained with a minimal amount of fine tuning requirements for possible models. We assume hierarchical mass matrices, dominated by the 3-3 element, with off-diagonal elements much smaller than the larger neighboring diagonal element. Characteristic features of this scenario are strong hierarchy in masses of right-handed neutrinos, and comparable contributions of both lighter right-handed neutrinos to the resulting left-handed neutrino …
The leptonic Higgs doublet model of neutrino masses is implemented with an A_4 discrete symmetry (the even permutation of 4 objects or equivalently the symmetry of the tetrahedron) which has 4 irreducible representations: 1, 1', 1'', and 3. The resulting spontaneous and soft breaking of A_4 provides a realistic model of charged-lepton masses as well as a nearly degenerate neutrino mass matrix. Phenomenological consequences at and below the TeV scale are discussed.
We revisit the possibility of generating non-zero reactor mixing angle in a scenario where there is a sterile neutrino at the eV scale apart from the usual three sub-eV scale active neutrinos. We show that the $3\times3$ active neutrino mass matrix can possess a $μ-τ$ symmetry and can still be consistent with non-zero value of the reactor mixing angle $θ_{13}$, if this $μ-τ$ symmetry is broken in the sterile neutrino sector. We first propose a simple model based on the discrete flavour symmetry $A_4 \times Z_3 \times Z^{\prime}_3$ to realise such a scenario and then numerically evaluate the co…
Neutrino flavor mixing is explained within the recently proposed low-scale minimal linear seesaw model of neutrino mass generation, a variant of the standard linear seesaw led by a Dirac pair of extra sterile neutrinos which is odd under a discrete $Z_2$ symmetry and has a mass at or below the GeV scale. The tri-bimaximal mixing and its deviations are derived straightforwardly on the basis of the symmetry between $μ$ and $τ$ flavors, without introducing non-abelian discrete flavor symmetries in the first place.
Large neutrino mixing angles suggest that the Yukawa sector is invariant under permutations of the fermion families. This S_{3} permutation symmetry is broken at a large energy scale but much below the unification scale. Assuming that the lepton mass matrix is approximately diagonal, all neutrino mixing angles naturally come from the breaking of S_{3}-> S_{2}. In the neutrino sector, S_{2} remains (approximately) unbroken. As a consequence, we have a large atmospheric neutrino angle and U_{e3}=0. The S_{3} symmetry at the unification scale can also explain the large solar mixing angle. We give…
We show that it is possible to fully determine the neutrino mass spectrum from two-zero textures of the neutrino mass matrix. As a consequence, definite predictions can be obtained for the neutrinoless double beta decay.
We study the effects of breaking S3 symmetry in the neutrino mass matrix for the masses and mixing matrix of neutrinos. At zeroth order the model gives degenerate neutrino masses and accommodates tribimaximal mixing. We introduce perturbations in terms of a small and complex parameter. The perturbations are introduced in a manner such that the S3 symmetry is broken by its elements in the same representation. Successive perturbations introduce mass splitting, sizable non-zero reactor mixing angle and CP violation. This scheme of breaking S3 symmetry can reproduce a relatively large reactor mixi…
The gauge model with $SO(3)_{F}$ flavor symmetry and three Higgs triplets is studied. We show how the intriguing nearly degenerate neutrino mass and bi-maximal mixing scenario comes out naturally after spontaneous breaking of the symmetry. The hierarchy between the neutrino mass-squared differences, which is needed for reconciling both solar and atmospheric neutrino data, is naturally resulted from an approximate permutation symmetry. The model can also lead to interesting phenomena on lepton-flavor violations via the $SO(3)_{F}$ gauge interactions.
We propose a model where Dirac neutrino mass is obtained from small vacuum expectation value (VEV) of neutrino-specific Higgs doublet without fine-tuning problem. The small VEV results from a seesaw-like formula with the high energy scale identified as the Peccei-Quinn (PQ) symmetry breaking scale. Axion can be introduced {\it à la} KSVZ or DFSZ. The model suggests neutrino mass, solution to the strong CP problem, and dark matter may be mutually interconnected.
We explore the consequences of the neutrino mass matrix having a hidden $\mathcal{Z}_2$ symmetry and one zero eigenvalue. When implemented, these two conditions give relations among the mixing angles. In addition, fitting these relations to the existing oscillation data allows limits to be placed on the parameter of the symmetry.
We consider triplet Higgs model with $A_4$ symmetry to generate the neutrino mass matrix. The tribimaximal form of the neutrino mixing matrix can be naturally obtained. Imposing the neutrino oscillation data, we show that 1) both normal and inverted mass hierarchy are allowed, 2) there is a lower bound on the lightest neutrino mass and the effective mass for neutrinoless double beta decay, 3) the non-vanishing $þ_{13}$ can be accommodated by considering small perturbation, 4) $þ_{\rm atm}$ should be very close to $π/4$ even after perturbation. }
We consider a U(1)' gauge symmetry acting on three generations of right-handed neutrinos. The U(1)' symmetry is broken at the TeV scale and its remnant discrete symmetry makes one of the right-handed neutrinos stable. As a natural consequence of the anomaly cancellation, the neutrino mass matrix consists of a combination of Type I (TeV scale) seesaw and radiative correction. The stable right-handed neutrino communicates with the Standard Model via s-channel exchange of the Higgs field and the U(1)' gauge boson, so that the observed relic density for dark matter is obtained in a wide range of t…
Heavy singlet neutrinos admit Majorana masses which are not possible for the Standard Model particles. This suggest new possibilities for generating the masses and mixing angles of light neutrinos. We present a model of neutrino physics which combines the source of lepton number violation with the flavor symmetry responsible for the hierarchy in the charged lepton and quark sector. This is accomplished by giving the scalar field effecting the lepton number violation a nonzero charge under the horizontal flavor symmetry. We find an economical model which is consistent with the measured values o…
The inverse seesaw mechanism with three pairs of gauge-singlet neutrinos offers a natural interpretation of the tiny masses of three active neutrinos at the TeV scale. We combine this picture with the newly-proposed Friedberg-Lee (FL) symmetry in order to understand the observed pattern of neutrino mixing. We show that the FL symmetry requires only two pairs of the gauge-singlet neutrinos to be massive, implying that one active neutrino must be massless. We propose a phenomenological ansatz with broken FL symmetry and exact μ-τsymmetry in the gauge-singlet neutrino sector and obtain the tri-bi…
