Minimal Extended Seesaw Research Articles

Neutrino Phenomenology and keV Dark Matter in the Two-Higgs Doublet Model with A4 Symmetry

Abstract We propose a minimal extended seesaw scheme based on the discrete symmetry $A_4\times Z_4\times Z_2\times Z_8$, which can successfully address neutrino phenomenology and keV sterile neutrino dark matter. The lepton mass hierarchy is naturally achieved. Active neutrino mixing angles can reached the best-fit points with the predictive Dirac CP violation phase. The active–sterile mixing matrix elements are small enough to access the observed cosmological dark matter abundance constraint with keV sterile neutrino dark matter. The effective neutrino masses are predicted to be in the ranges of the recent experimental limits.

Leptogenesis and eV scale sterile neutrino

We consider the minimal extended seesaw model that can accommodate an eV scale sterile neutrino. The scenario also includes three heavy right-handed neutrinos in addition to the light-sterile neutrino. In this model, the active-sterile mixing acts as nonunitary parameters. If the values of these mixing angles are of $\mathcal{O}(0.1)$, the model introduces deviation of the Pontecorvo-Maki-Nakagawa-Sakata matrix from unitarity to this order. We find that the oscillation data from various experiments impose an upper bound on the lightest heavy neutrino mass scale as $\ensuremath{\sim}{10}^{11}\text{ }\text{ }\mathrm{GeV}$ in the context of this model. We study vanilla leptogenesis in this scheme, where the decay of the heavy right-handed neutrinos in the early Universe can give rise to the observed baryon asymmetry. Here, even though the eV scale sterile neutrino does not participate directly in leptogenesis, its effect is manifested through the nonunitary effects. We find that the parameter space that can give rise to successful leptogenesis is constrained by the bounds on the active-sterile mixing as obtained from the global analysis.

Five-zero texture in neutrino-dark matter model within the framework of minimal extended seesaw

We study a model of neutrino and dark matter within the framework of a minimal extended seesaw (MES). This model is based on A4 flavour symmetry along with the discrete Z3×Z4 symmetry to stabilize the dark matter and construct desired mass matrices for neutrino mass. Five-zero textures are imposed in the final 4×4 active-sterile mass matrix, which significantly reduces the free parameter in the model. Three right-handed neutrinos were considered, two of them have degenerate masses which help us to achieve baryogenesis via resonant leptogenesis. A singlet fermion (sterile neutrino) with mass ∼O(eV) is also considered, and we are able to put bounds on active-sterile mixing parameters via neutrino oscillation data. Resonant enhancement of lepton asymmetry is studied at the TeV scale, where we discuss a few aspects of baryogenesis considering the flavour effects. The possibility of improvement in effective mass from 0νββ in the presence of a single generation of sterile neutrino flavour is also studied within the fermion sector. In the scalar sector, the imaginary component of the complex singlet scalar (χ) is behaving as a potential dark matter candidate and simultaneously the real part of the complex scalar is associated with the fermion sector for sterile mass generation.

Effect of Sterile Neutrino on Low-Energy Processes in Minimal Extended Seesaw With Δ(96) Symmetry and TM1 Mixing

We study the effect of sterile neutrino on some low-scale processes in the framework of the minimal extended seesaw (MES). MES is the extension of the seesaw mechanism with the addition of sterile neutrino of intermediate mass. The MES model in this work is based on Δ(96) ×C2×C3flavor symmetry. The structures of mass matrices in the framework lead toTM1mixing withμ–τsymmetry. The model predicts the maximal value of the Dirac CP phase. We carry out our analysis to study the new physics contributions from the sterile neutrino to different charged lepton flavor violation (cLFV) processes involving muon and tau leptons as well as neutrinoless double beta decay (0νββ). The model predicts normal ordering (NO) of neutrino masses, and we perform the numerical analysis considering normal ordering (NO) only. We find that a heavy sterile neutrino can lead to cLFV processes that are within the reach of current and planned experiments. The sterile neutrino present in our model is consistent with the current limits on the effective neutrino mass set by 0νββexperiments.

Realization of the minimal extended seesaw mechanism and the TM2 type neutrino mixing

We construct a neutrino mass model based on the flavour symmetry group A4×C4×C6×C2 which accommodates a light sterile neutrino in the minimal extended seesaw (MES) scheme. Besides the flavour symmetry, we introduce a U(1) gauge symmetry in the sterile sector and also impose CP symmetry. The vacuum alignments of the scalar fields in the model spontaneously break these symmetries and lead to the construction of the fermion mass matrices. With the help of the MES formulas, we extract the light neutrino masses and the mixing observables. In the active neutrino sector, we obtain the TM2 mixing pattern with non-zero reactor angle and broken μ-τ reflection symmetry. We express all the active and the sterile oscillation observables in terms of only four real model parameters. Using this highly constrained scenario we predict {sin}^2{theta}_{23}={0.545}_{-0.004}^{+0.003},sin delta =-{0.911}_{-0.005}^{+0.006},{left|{U}_{e4}right|}^2={0.029}_{-0.008}^{+0.009},{left|{U}_{mu 4}right|}^2={0.010}_{-0.003}^{+0.003}kern0.5em mathrm{and}kern0.5em {left|{U}_{tau 4}right|}^2={0.006}_{-0.002}^{+0.002} which are consistent with the current data.

Phenomenology of keV sterile neutrino in minimal extended seesaw

We explore the possibility of a single generation of keV scale sterile neutrino [Formula: see text] as a dark matter candidate within the minimal extended seesaw (MES) framework and its influence in neutrinoless double beta decay [Formula: see text] study. Three hierarchical right-handed neutrinos were considered to explain neutrino mass. We also address baryogenesis via the mechanism of thermal leptogenesis considering the decay of the lightest RH neutrino to a lepton and Higgs doublet. A generic model based on [Formula: see text] flavor symmetry is constructed to explain both normal and inverted hierarchy mass pattern of neutrinos. Significant results on effective neutrino masses are observed in presence of sterile mass [Formula: see text] and active-sterile mixing [Formula: see text] in [Formula: see text]. Results from [Formula: see text] give stringent upper bounds on the active-sterile mixing matrix element. To establish sterile neutrino as dark matter within this model, we checked decay width and relic abundance of the sterile neutrino, which restricted sterile mass [Formula: see text] within some definite bounds. Constrained regions on the CP phases and Yukawa couplings are obtained from [Formula: see text] and baryogenesis results. Co-relations among these observable are also established and discussed within this framework.

Minimal extended seesaw and group symmetry realization of two-zero textures of neutrino mass matrices

We study the phenomenology of two-zero textures of Mν4×4 neutrino mass matrices in the minimal extended seesaw (MES) mechanism. Mν4×4 involves 3×3 Dirac neutrino mass matrix (MD), 3×3 right-handed Majorana neutrino mass matrix MR and 1×3 matrix MS that couples the singlet field ‘S’ with the right-handed neutrinos. We consider the phenomenologically predictive cases (5+3) and (6+2) schemes for zero textures of MD and MR of 3×3 active sector of Mν4×4 along with admissible one or two-zero textures of MS. Although there is a large number of combinations of MD,MR and MS leading to the desired two-zero textures, S3 group transformations between the different zero textures of MD,MR and MS reduce them to a small number of basic combinations. In MES, Mν4×4 should be a matrix of rank 3, so we have 12 two-zero textures of neutrino mass matrices of rank 3 out of total 15 two-zero textures of neutrino mass matrices. In realization of the two-zero textures in (5+3) scheme we have obtained a number of correlations among the neutrino mass matrix elements mij, while none of the two-zero textures could be realized in the (6+2) scheme. The viability of each of the realizable textures is checked by plotting the scatter plots of their respective correlations under the current neutrino oscillation data. We have analysed the role played by the Dirac and Majorana CP phases for each of the textures. For constrained ranges of CP phases we also draw scatter plots for Jarlskog invariant (JCP) and effective electron neutrino mass |mββ|. In our study the viable textures are finally realized by Z8 Abelian group symmetry by extending the Standard Model to include few scalar fields.

Phenomenological study of neutrino mass, dark matter and baryogenesis within the framework of minimal extended seesaw

We study a model of neutrino and dark matter within the framework of a minimal extended seesaw. This framework is based on A4 flavor symmetry along with the discrete Z4 symmetry to stabilize the dark matter and construct desired mass matrices for neutrino mass. We use a non-trivial Dirac mass matrix with broken μ − τ symmetry to generate the leptonic mixing. A non-degenerate mass structure for right-handed neutrinos is considered to verify the observed baryon asymmetry of the Universe via the mechanism of thermal Leptogenesis. The scalar sector is also studied in great detail for a multi-Higgs doublet scenario, considering the lightest Z4-odd as a viable dark matter candidate. A significant impact on the region of DM parameter space, as well as in the fermionic sector, are found in the presence of extra scalar particles.

Phenomenological study of texture zeros of fermion mass matrices in minimal extended seesaw mechanism

We study the two-zero textures in in minimal extended type-I seesaw (MES) mechanism with incorporating one extra gauge singlet field ‘S’. has (3×3)Dirac neutrino mass matrix MD, (3×3) right-handed Majorana mass matrix MR and (1×3) row matrix MS. For our study we consider 5 zeros in MD and 4 zeros in MR, (5+4) scheme, along with one-zero textures of MS to arrive at the two-zero textures of . We find that out of 15 allowed two-zero textures, only 9 textures can be realized under (5+4) scheme. We also find that different textures of MD, MR and MS are related to each other through S3 permutation group which leads to only a few basic combinations of MD, MR and MS. We present all the combinations of MD, MR and MS and show their interconvertability nature due to S3 symmetry between them.

Understanding of two-zero textures of neutrino mass matrices in minimal extended seesaw mechanism and their symmetry realization

We study the texture zeros of [Formula: see text] neutrino mass matrices [Formula: see text] in the minimal extended type-I seesaw (MES) mechanism, incorporating one extra gauge singlet field “[Formula: see text]”. The [Formula: see text] MES model deals with [Formula: see text] [Formula: see text], [Formula: see text] [Formula: see text] and [Formula: see text] mass matrix [Formula: see text] which couples the right-handed neutrinos and the singlet field “[Formula: see text]”. We carry out the mapping of all possible zero textures of [Formula: see text], [Formula: see text] and [Formula: see text] with the restriction to phenomenologically predictive cases having total eight zeros of [Formula: see text] and [Formula: see text] studied in the literature. If [Formula: see text], the sterile neutrino mass, is subject to any limit, further block diagonalization of [Formula: see text] shall not be allowed to reduce it to a [Formula: see text] matrix. In [Formula: see text] [Formula: see text] scenario, the study of texture zero is totally different and interesting. With this motivation, we consider the [Formula: see text] scheme where the digits of the pair represent the number of zeros of [Formula: see text] and [Formula: see text], respectively, along with the one/two-zero textures of [Formula: see text]. There are a large number of possibilities of zeros of fermion mass matrices, but the implementation of [Formula: see text] transformations reduces it to a very minimum number of basic structures. As the [Formula: see text] MES matrix is a matrix of rank 3, so we consider only those textures with two zeros which are of rank 3 whereby the number of feasible zero textures reduces to 12, out of 15. On realizing these 12 textures under MES mechanism with [Formula: see text] picture, we arrive at certain correlations for each texture. We examine the viability of each texture by scanning their respective correlations under recent neutrino oscillation data. Also, we discuss the interplay of Dirac and Majorana CP phases in determining the viability of a texture. The allowed two-zero textures are finally realized using a discrete Abelian flavor symmetry group [Formula: see text] with the extension of Standard Model to include some scalar fields.

Active and sterile neutrino phenomenology with A4 based minimal extended seesaw

We study a model of neutrino within the framework of minimal extended seesaw (MES), which plays an important role in active and sterile neutrino phenomenology in (3+1) scheme. The A4 flavor symmetry is augmented by additional Z4×Z3 symmetry to constraint the Yukawa Lagrangian of the model. We use non-trivial Dirac mass matrix, with broken μ−τ symmetry, as the origin of leptonic mixing. Interestingly, such structure of mixing naturally leads to the non-zero reactor mixing angle θ13. Non-degenerate mass structure for right-handed neutrino MR is considered so that we can further extend our study to Leptogenesis. We have also considered three different cases for sterile neutrino mass, MS to check the viability of this model, within the allowed 3σ bound in this MES framework.

Compatibility of A_{4} flavour symmetric minimal extended seesaw with (3+1) neutrino data

Motivated by the recent resurrection of the evidence for an eV scale sterile neutrino from the MiniBooNE experiment, we revisit one of the most minimal seesaw model known as the minimal extended seesaw that gives rise to a 3+1 light neutrino mass matrix. We consider the presence of A_{4} flavour symmetry which plays a non-trivial role in generating the structure of the neutrino mass matrix. Considering a diagonal charged lepton mass matrix and generic vacuum alignments of A_{4} triplet flavons, we classify the resulting mass matrices based on their textures. Keeping aside the disallowed texture zeros based on earlier studies of 3+1 neutrino textures, we categorise the remaining ones based on texture zeros, mu –tau symmetry in the 3times 3 block and hybrid textures. After pointing out the origin of such 3+1 neutrino textures to A_{4} vacuum alignments, we use the latest 3+1 neutrino oscillation data and numerically analyse the texture zeros and mu –tau symmetric cases. We find that a few of them are allowed from each category predicting interesting correlations between neutrino parameters. We also find that all of these allowed cases prefer normal hierarchical pattern of light neutrino masses over inverted hierarchy.

Study of texture zeros of fermion mass matrices in minimal extended seesaw mechanism and symmetry realization

In our work, we study the texture zeros of [Formula: see text] in the minimal extended type-I seesaw (MES) with incorporating one extra gauge singlet field “[Formula: see text]”. The MES models deal with the Dirac neutrino mass matrix [Formula: see text], the right-handed Majorana mass matrix [Formula: see text] and the sterile neutrino mass matrix [Formula: see text]. We carry out the mapping of all possible zero textures of [Formula: see text], [Formula: see text] and [Formula: see text] for phenomenologically predictive cases having total eight zeros of [Formula: see text] and [Formula: see text] studied in the literature. With this motivation, we consider (a) [Formula: see text] scheme, (b) [Formula: see text] scheme and (c) [Formula: see text] scheme, where the digits of a pair represent the number of zeros of [Formula: see text] and [Formula: see text], respectively along with the one zero and two zero textures of [Formula: see text]. There are a large number of possibilities of zeros of fermion mass matrices but the implementation of [Formula: see text] transformations reduces it to a very minimum number of basic structures. Interestingly out of four allowed one zero textures of [Formula: see text] without sterile neutrino, only three cases ([Formula: see text], [Formula: see text] and [Formula: see text]) are allowed in MES mechanism for the [Formula: see text] and [Formula: see text] schemes. We find some correlations for different combination of [Formula: see text], [Formula: see text] and [Formula: see text] on enforcement of zeros. We examined all the correlations under the recent neutrino oscillation data and find that only [Formula: see text] survives while both [Formula: see text] and [Formula: see text] are ruled out. Interestingly the one zero textures inherently represent the inverted hierarchy of the mass ordering of light neutrinos. No two zero textures of [Formula: see text] survive in MES although there are a number of allowed structures phenomenologically. The allowed texture zeros are finally realized using a discrete Abelian flavor symmetry group [Formula: see text] with the extension of standard model to include some scalar fields.

Light sterile neutrino in the minimal extended seesaw

Motivated by the recent observations on sterile neutrinos, we present a minimal extension of the canonical type-I seesaw by adding one extra singlet fermion. After the decoupling of right-handed neutrinos, an eV-scale mass eigenstate is obtained without the need of artificially inserting tiny mass scales or Yukawa couplings for sterile neutrinos. In particular, the active-sterile mixing is predicted to be of the order of 0.1. Moreover, we show a concrete flavor A4 model, in which the required structures of the minimal extended seesaw are realized. We also comment on the feasibility of accommodating a keV sterile neutrino as an attractive candidate for warm dark matter.