We study a model which generates Majorana neutrino masses at tree-level via low-energy effective operator with mass-dimension-9. Introduction of such a higher dimensional operator brings down the lepton number violating mass scale to TeV making such model potentially testable at present or near future colliders. This model possesses several new $SU(2)_L$ fermionic multiplets, in particular, three generations of triplets, quadruplets and quintuplets, and thus a rich phenomenology at the LHC. As the lepton flavour violation arises very naturally in such setup, we put constraints on the Yukawa couplings and heavy fermion masses from the current experimental bounds on lepton flavour violating processes. We also obtain 95% CL lower bounds on the masses of the triplets, quadruplets and quintuplets using a recent CMS search for multilepton final states with 137 inverse femtobarn integrated luminosity data at 13 TeV center of mass energy. The possibility that the heavy fermions could be long-lived leaving disappearing charge track signatures or displaced vertex at the future colliders like LHeC, FCC-he, MATHUSLA, etc. is also discussed.
The simplest possibility to generate small Majorana neutrino masses is the seesaw mechanism. However, the smallness of the observed neutrino masses can also be understood, if neutrino masses are generated by higher-dimensional operators and/or at higher loop level. In this talk recent work on systematic classifications of higher-dimensional and radiative neutrino mass models is summarized. Two particular classes of special genuine loop diagrams, i.e. diagrams which can lead to genuine neutrino mass models only under some specific, well-defined conditions, are also discussed.
As an extension of our previous work in the seesaw mechanism, we analyze the influence of $U_{e3}$ on the properties (masses and mixing) of the RH Majorana neutrinos in three flavors. The quasidegenerate light neutrinos case is also considered. Assuming the hierarchical Dirac neutrino masses, we find the heavy Majorana neutrino mass spectrum is either hierarchical or partial degenerate if $θ_{23}^ν$ is large. We show that degenerate RH Majorana masses correspond to maximal RH mixing angle while hierarchical ones correspond to the RH mixing angles which scale linearly with the mass ratios of th…
We discuss the phenomenology of type-II seesaw by extending the Standard Model with additional Higgs doublets and scalar triplets additionally invoked with $Δ(27)$ flavor symmetry for the explanation of non-zero neutrino masses and mixings, matter-antimatter asymmetry and lepton flavor violation. The non-zero neutrino masses can be realized via type-II seesaw mechanism by introducing scalar triplets transforming as triplets under $Δ(27)$ while we add additional $SU(2)_L$ scalar doublets to have correct charge lepton masses. We further demonstrate with detailed numerical analysis in agreement w…
We study a model of neutrino and dark matter within the framework of a minimal extended seesaw. This framework is based on $A_4$ flavor symmetry along with the discrete $Z_4$ 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 mult…
We analyse the phenomenology of a model of neutrino masses inspired by $\mathrm{E}_{6}$ GUT unification in which the exotic neutrinos can be present at low scales. The model introduces vector-like isosinglet down-type quarks, vector-like isodoublet leptons, neutrino singlets and two $Z'$ bosons. The seesaw mechanism can be achieved with exotic neutrino masses as low as 100 GeV and Yukawa couplings of order $10^{-3}$. We find that the lightest $Z'$ boson mass is required to be above 2.8 TeV, the exotic quark masses are required to be above 1.3 TeV (810 GeV) if they are collider stable (promptly…
We propose a viable theory based on the $SU(3)_C\times SU(3)_L\times U(1)_X$ gauge group supplemented by the $S_4$ discrete group together with other various symmetries, whose spontaneous breaking gives rise to the current SM fermion mass and mixing hierarchy. In the proposed theory the small light active neutrino masses are generated from a linear seesaw mechanism mediated by three Majorana neutrinos. The model is capable of reproducing the experimental values of the physical observables of both quark and lepton sectors. Our model is predictive in the quark sector having 9 effective parameter…
We summarize the phenomenological constraints on seesaw scenarios defined at the TeV scale and provide a simple extension of the Standard Model which naturally leads to a testable mechanism of neutrino mass generation.
The type-III seesaw seems to explain the very minuteness of neutrino masses readily and naturally. The high-energy see-saw theories usually involve a larger number of effective parametres than the physical and measurable parametres appearing in the low-energy neutrino phenomenology. Casas-Ibarra parametrisation facilitates to encode the information lost in integrating the heavy fermions out in an arbitrary complex orthogonal matrix. The CMS collaboration has already searched for triplet fermions in the type-III seesaw model with only one generation of triplet fermion flavour democratically dec…
We study the constraints on a minimal supersymmetric seesaw model imposed by neutrino data, charged lepton flavor violation, thermal leptogenesis and perturbativity. We show that it is possible to constrain the three heavy Majorana neutrino masses as well as the complex Yukawa coupling matrix. Our results provide a first step towards a seesaw benchmark model for further phenomenological studies and model building.
Two important features of TeV-scale radiative seesaw models, in which tiny neutrino masses are generated at the quantum level, are an extended scalar (Higgs) sector and the Majorana nature. We study phenomenological aspects of these models at the ILC. It is found that the Majorana nature of the models can be tested directly via the electron-positron and electron-electron collision experiments.
We study the inverse seesaw mechanism for neutrino masses and phenomenological consequences in the context of conformal electro-weak symmetry breaking. The main difference to the usual case is that all explicit fermion mass terms including Majorana masses for neutrinos are forbidden. All fermion mass terms arise therefore from vacuum expectation values of suitable scalars times some Yukawa couplings. This leads to interesting consequences for model building, neutrino mass phenomenology and the Dark Matter abundance. In the context of the inverse seesaw we find a favoured scenario with heavy ps…
We extend the Type I and Type III seesaw mechanisms to generate neutrino masses within the left-right symmetric theories where parity is spontaneously broken. We construct a next to minimal left-right symmetric model where neutrino masses are generated through a variant $double$ seesaw mechanism. In our model at least one of the triplet fermions and the right handed neutrinos are at TeV scale and others are heavy. The phenomenological aspects and testability of the TeV scale particles at collider experiments are discussed. The decays of heavy fermions leading to leptogenesis are pointed out.
We consider a supersymmetric type III seesaw, where the additional heavy states are embedded into complete SU(5) representations to preserve gauge coupling unification. Complying with phenomenological and experimental constraints strongly tightens the viable parameter space of the model. In particular, one expects very characteristic signals of lepton flavour violation both at low-energies and at the LHC, which offer the possibility of falsifying the model.
In minimal trinification models light neutrino masses can be generated via a radiative see-saw mechanism, where the masses of the right-handed neutrinos originate from loops involving Higgs and fermion fields at the unification scale. This mechanism is absent in models aiming at solving or ameliorating the hierarchy problem, such as low-energy supersymmetry, since the large seesaw-scale disappears. In this case, neutrino masses need to be generated via a TeV-scale mechanism. In this paper, we investigate an inverse seesaw mechanism and discuss some phenomenological consequences.
In the presence of large extra dimensions, the fundamental scale could be as low as a few TeV. This yields leptogenesis and seesaw at a TeV scale. Phenomenologically two TeV-scale Majorana fermions with a small mass split can realize a resonant leptogenesis whereas a TeV-scale Higgs triplet with a small trilinear coupling to the standard model Higgs doublet can give a verifiable seesaw. We propose an interesting scenario where the small parameters for the resonant leptogenesis and the type-II seesaw can be simultaneously generated by the propagation of lepton number violation from distant bran…
We study the zero textures of the Yukawa matrices in the minimal extended type-I seesaw (MES) model which can give rise to $\sim$ eV scale sterile neutrinos. In this model, three right handed neutrinos and one extra singlet $S$ are added to generate a light sterile neutrino. The light neutrino mass matrix for the active neutrinos, $ m_ν$, depends on the Dirac neutrino mass matrix ($ M_{D} $), Majorana neutrino mass matrix ($ M_{R} $) and the mass matrix ($ M_{S} $) coupling the right handed neutrinos and the singlet. The model predicts one of the light neutrino masses to vanish. We systematica…
We propose a novel supersymmetric unified scenario of the triplet seesaw mechanism where the exchange of the heavy triplets generates both neutrino masses and soft supersymmetry breaking terms. Our framework is very predictive since it relates neutrino mass parameters, lepton flavour violation in the slepton sector, sparticle and Higgs spectra and electroweak symmetry breakdown. The phenomenological viability and experimental signatures in lepton flavor violating processes are discussed.
The non-unitarity effects in the leptonic flavor mixing are regarded as one of the generic features of the type-I seesaw model. Therefore, we explore these effects in the TeV-scale type-I seesaw model, and show that there exist non-trivial correlations among the non-unitarity parameters, stemming from the typical flavor structure of the low-scale seesaw model. In general, it follows from analytical discussions and numerical results that all the six non-unitarity parameters are related to three model parameters, while the widely studied parameters η_{eτ} and η_{μτ} cannot be phenomenologically …
We review and update the current phenomenological constraints on minimal type I seesaw extensions of the Standard Model in which New Physics content can be probed at the electroweak scale. In this class of models, the flavour structure of the neutrino Yukawa couplings is determined by the requirement of reproducing neutrino oscillation data. The strongest constraints on the seesaw parameter space are imposed by the very recent upper limit on μ --> e γ decay rate. Searches of non-standard Higgs boson decays into a light and a heavy neutrino may also provide and independent test of these seesaw …
We extend the Type I seesaw and suggest a $new$ seesaw mechanism to generate neutrino masses within the left-right symmetric theories where parity is spontaneously broken. We construct a next to minimal left-right symmetric model where neutrino masses are determined irrespective of the B-L breaking scale and call it the $new$ seesaw mechanism. In this scenario B-L scale can be very low. This makes B-L gauge boson and the quasi-Dirac $heavy$ leptons very light. These TeV scale particles could have large impact on lepton flavor and CP violating processes. We also shed light on the phenomenologic…
The Minimal Flavor Violation hypothesis (MFV) is extended to the R-parity violating MSSM, supplemented with a simple seesaw mechanism. The requirement of MFV is shown to suppress lepton and baryon-number violating couplings sufficiently to pass all experimental bounds, in particular those for proton decay, and is thus a viable alternative to R-parity. The phenomenological consequences for FCNC, LFV and colliders are briefly discussed. Typically, MFV predicts sizeable baryon-number violation in some characteristic channels, like single stop resonant production.
The Majorana nature of neutrinos is strongly motivated from the theoretical and phenomenological point of view. A plethora of neutrino mass models, known collectively as Seesaw models, exist that could generate both a viable neutrino mass spectrum and mixing pattern. They can also lead to rich, new phenomenology, including lepton number non-conservation as well as new particles, that may be observable at collider experiments. It is therefore vital to search for such new phenomena and the mass scale associated with neutrino mass generation at high energy colliders. In this review, we consider a…
Knowledge of the mechanism of neutrino mass generation would help understand a lot more about Lepton Number Violation (LNV), the cosmological evolution of the Universe, or the evolu tion of astronomical objects. Here we propose a verifiable and viable extension of the Standard model for neutrino mass generation, with a low-scale seesaw mechanism via LNV condensation in the sector of sterile neutrinos. To prove the concept, we analyze a simplified model of just one single family of elementary particles and check it against a set of phenomenological constraints coming from electroweak symmetry b…
Inverse seesaw is a genuine TeV scale seesaw mechanism. In it active neutrinos with masses at eV scale requires lepton number be explicitly violated at keV scale and the existence of new physics, in the form of heavy neutrinos, at TeV scale. Therefore it is a phenomenologically viable seesaw mechanism since its signature may be probed at the LHC. Moreover it is successfully embedded into gauge extensions of the standard model as the 3-3-1 model with the right-handed neutrinos. In this work we revisit the implementation of this mechanism into the 3-3-1 model and employ deep learning analysis to…
We investigate scaling ansatz with texture zeros within the framework of linear seesaw mechanism. In this variant of seesaw mechanism a simplified expression of effective neutrino mass matrix $m_ν$ containing two Dirac type matrices ($m_D$ and $m_{DS}$) and one Majorana type matrix ($m_{RS}$) is obtained by virtue of neglecting the global $U(1)_L$ symmetry breaking term in the mass term of the Lagrangian. Along with the charged lepton mass matrix, the matrix $m_{RS}$ too, is chosen in a diagonal basis whereas a scaling relation is incorporated in $m_D$ and $m_{DS}$ with different scale factors…
We discuss phenomenological consequences of some class of supersymmetric seesaw models in which the right-handed (s)neutrino mass is given to be TeV scale. In this scenario, scalar trilinear interaction of Higgs-slepton-(right-handed) sneutrino is enhanced. We show that the 1-loop correction by sneutrino exchange to the lightest Higgs boson mass destructively interferes with top-stop contributions in the minimal SUSY Standard Model. We find that a decay of charged Higgs boson into sneutrino and charged slepton is sizably enhanced and hence it gives rise to a distinctive signal at future collid…
Two Higgs Doublet Models (2HDM) are popular extensions of the Standard Model for several reasons, but do not explain neutrino masses. In this work, we investigate how one can incorporate neutrino masses within the framework of the 2HDM-U(1), where U(1) is an abelian gauge symmetry used to nicely address the absence of flavor changing neutral currents in 2HDM. In particular, we explore realizations of the type I and type II seesaw since they are mechanisms that we dote on for being able to generate elegantly small active neutrino masses. We show that one can build several models featuring type …
The three electroweak doublet neutrinos $ν_{e,μ,τ}$ of the Standard Model may acquire small seesaw masses, using either three Majorana fermion singlets $N$ or three Majorana fermion triplets $(Σ^+,Σ^0,Σ^-)$. It is well-known that the former accommodates the U(1) gauge symmetry $B-L$. It has also been shown some years ago that the latter supports a new $U(1)_X$ gauge symmetry. Here we study two variations of this $U(1)_X$, one for two $N$ and one $Σ$, the other for one $N$ and two $Σ$. Phenomenological consequences are discussed.
Given its briefness and predictability, the minimal seesaw -- a simplified version of the canonical seesaw mechanism with only two right-handed neutrino fields -- has been studied in depth and from many perspectives, and now it is being pushed close to a position of directly facing experimental tests. This article is intended to provide an up-to-date review of various phenomenological aspects of the minimal seesaw and its associated leptogenesis mechanism in neutrino physics and cosmology. Our focus is on possible flavor structures of such benchmark seesaw and leptogenesis scenarios and confro…
We propose new mechanisms for small neutrino masses based on clockwork mechanism. The Standard Model neutrinos and lepton number violating operators communicate through the zero mode of clockwork gears, one of the two couplings of the zero mode is exponentially suppressed by clockwork mechanism. Including all known examples for the clockwork realization of the neutrino masses, different types of models are realized depending on the profile and chirality of the zero mode fermion. Each type of realization would have phenomenologically distinctive features with the accompanying heavy neutrinos.
We provide a scenario where naturally small and calculable neutrino masses arise from a supersymmetry breaking renormalization-group-induced vacuum expectation value. We adopt a minimal supergravity scenario without ad hoc supersymmetric mass parameters. The lightest supersymmetric particle can be an isosinglet scalar neutrino state, potentially viable as WIMP dark matter through its Higgs new boson coupling. The scenario leads to a plethora of new phenomenological implications at accelerators including the Large Hadron Collider.
Parametrization of the neutrino mass matrix in terms of well-known measured quantities is an attractive way to obtain a phenomenologically viable form. We propose a model of neutrino mass matrix based on type-II seesaw mechanism adhering the concept of badly broken symmetry. Two of the mixing angles are coming out as $θ_{23}\sim46.08^{\circ}$, $θ_{13}\sim8.69^{\circ}$. However, to accommodate the other oscillation parameters, we further add an extra doublet and the neutrino masses are generated through the Zee mechanism at the one loop level, and the modified model can admit all the extant dat…
Discrete symmetries being preferred to explain the neutrino phenomenology, we chose the simplest $S_3$ group and explore the implication of its modular form on neutrino masses and mixing. Non-trivial transformations of Yukawa couplings under this symmetry, make the model phenomenologically interesting by reducing the requirement of multiple scalar fields. This symmetry imposes a specific flavor structure to the neutrino mass matrix within the framework of less frequented type III seesaw mechanism and helps to explore the neutrino mixing consistent with the current observation. Apart, we also e…
Alternative renormalizable minimal non-SUSY SO(10) GUT model is proposed. Instead of a ${\bf 126}$-dimensional Higgs field, a ${\bf 120}$-dimensional Higgs filed is ntroducedin addition to a ${\bf 10}$-dimensional Higgs field and plays a crucial role to reproduce the realistic charged fermion mass matrices. With contributions of ${\bf 120}$ Higgs field, the original Witten's scenario of inducing the right-handed Majorana neutrino mass through 2-loop diagrams becomes phenomenologically viable. This model inherits the nice features of the conventional renormalizable minimal SO(10) GUT model with…
We discuss the leptonic flavor structure generated by a brane shifted extra dimensional seesaw model with a single right handed neutrino in the bulk. In contrast to previous works, no unitarity approximation for the $3 \times 3$ submatrix has been employed. This allows to study phenomenological signatures such as lepton flavor violating decays. A strong prediction of the model, assuming CP conservation, are the ratios of flavor violating charged lepton decay and Z decay branching ratios which are correlated with the neutrino mixing angles and the neutrino mass hierarchy. Furthermore, it is pos…
A general feature of TeV-scale radiative seesaw models, in which tiny neutrino masses are generated via loop corrections, is an extended scalar (Higgs) sector. Another feature is the Majorana nature; e.g., introducing right-handed neutrinos with TeV-scale Majorana masses under the discrete symmetry, or otherwise introducing some lepton number violating interactions in the scalar sector. We study phenomenological aspects of these models at collider experiments. We find that, while properties of the extended Higgs sector of these models can be explored to some extent, the Majorana nature of the …
We consider a model of neutrino mass with a scalar triplet $(ξ^{++},ξ^+,ξ^0)$ assigned lepton number $L=0$, so that the tree-level Yukawa coupling $ξ^0 ν_i ν_j$ is not allowed. It is generated instead through the interaction of $ξ$ and $ν$ with dark matter and the soft breaking of $L$ to $(-1)^L$. We discuss the phenomenological implications of this model, including $ξ^{++}$ decay and the prognosis of discovering the dark sector at the Large Hadron Collider.
When a small vacuum expectation value of Higgs triplet ($v_Δ$) in the type-II seesaw model is required to explain neutrino oscillation data, a fine-tuning issue occurs on the mass-dimension lepton-number-violation (LNV) scalar coupling. Using the scotogenic approach, we investigate how a small LNV term is arisen through a radiative correction when an $Z_2$-odd vector-like lepton ($X$) and an $Z_2$-odd right-handed Majorana lepton ($N$) are introduced to the type-II seesaw model. Due to the dark matter (DM) direct detection constraints, the available DM candidate is the right-handed Majorana pa…
The gauging of the lepton flavour group is considered in the Standard Model context and in its extension with three right-handed neutrinos. The anomaly cancellation conditions lead to a Seesaw mechanism as underlying dynamics for all leptons; requiring in addition a phenomenologically viable setup leads to Majorana masses for the neutral sector: the type I Seesaw Lagrangian in the Standard Model case and the inverse Seesaw in the extended model. Within the minimal extension of the scalar sector, the Yukawa couplings are promoted to scalar fields in the bifundamental of the flavour group. The r…
There are no upper limits on the possible number of massive, singlet (right--handed) neutrinos that may participate in the seesaw mechanism, and some string constructions motivate seesaw models with up to O(100) right--handed neutrinos. In this case, the seesaw mass scale can be significantly higher than that in the traditional scheme with just 3 right--handed neutrinos. We consider the possible phenomenological implications of such models, in particular, for lepton-flavour violation and electric dipole moments. Since the neutrino masses depend on the Majorana mass scale linearly, while supers…
We consider the possibility of texture zeros in lepton mass matrices of the minimal left-right symmetric model (LRSM) where light neutrino mass arises from a combination of type I and type II seesaw mechanisms. Based on the allowed texture zeros in light neutrino mass matrix from neutrino and cosmology data, we make a list of all possible allowed and disallowed texture zeros in Dirac and heavy neutrino mass matrices which appear in type I and type II seesaw terms of LRSM. For the numerical analysis we consider those cases with maximum possible texture zeros in light neutrino mass matrix $M_ν$,…
We investigate charged lepton flavor violating (CFLV) processes in the `neutrinophilic Higgs+seesaw model', in which right-handed neutrinos couple only with an extra Higgs field which develops a tiny VEV and the right-handed neutrinos also have Majorana mass. The model realizes a seesaw mechanism around TeV scale without extremely small Dirac Yukawa couplings. A phenomenological feature of the model is CFLV processes induced by loop diagrams of the charged scalar particles and heavy neutrinos. Therefore, first we constrain the model's parameter space from the search for $μ\to eγ$. Next, we pre…
We prove that - even at a low TeV scale - the canonical seesaw mechanism can be naturally implemented in the exact solution of a particular 3-3-1 gauge model, since a very small alteration $ε$ in the parameter matrix of the Higgs sector is taken into account. Therefore, this new parameter can act as an appropriate mass source for neutrinos, while - due to the main parameter $a$ - all the previously achieved results in the exact solution of the model are recovered. Moreover, this mathematical artifice does separate the boson mass spectrum from the neutrino mass issue, hence giving more flexibil…
A unified mass matrix model of quarks and leptons with a seesaw-type form $M_f=m M_F^{-1} m$ is proposed on the basis of a non-standard Higgs scenario. The matrix $m$ is provided by U(3)-family nonet bosons $ϕ$, and the matrix $M_F$ is a mass matrix of heavy fermions $F_i$ corresponding to the ordinary fermions $f_i=ν_i,e_i,u_i,d_i$ ($i=1,2,3$). It is shown that a Higgs potential of $ϕ$ with a broken U(3)-family symmetry leads to a desirable charged lepton mass formula when $M_E\propto {\bf 1}$. Then, phenomenologically desirable forms of heavy quark mass matrices $M_Q$ ($Q=U,D$) are investiga…
Neutrino mass generation through the Higgs mechanism not only suggests the need to reconsider the physics of electroweak symmetry breaking from a new perspective, but also provides a new theoretically consistent and experimentally viable paradigm. We illustrate this by describing the main features of the electroweak symmetry breaking sector of the simplest type-II seesaw model with spontaneous breaking of lepton number. After reviewing the relevant "theoretical" and astrophysical restrictions on the Higgs sector, we perform an analysis of the sensitivities of Higgs boson searches at the ongoin…
Stimulated by the phenomenological success of the universal seesaw mass matrix model, where the mass terms for quarks and leptons f_i (i=1,2,3) and hypothetical super-heavy fermions F_i are given by \bar{f}_L m_L F_R +\bar{F}_L m_R f_R + \bar{F}_L M_F F_R + h.c. and the form of M_F is democratic on the bases on which m_L and m_R are diagonal, the following model is discussed: The mass terms M_F are invariant under the permutation symmetry S_3, and the mass terms m_L and m_R are generated by breaking the S_3 symmetry spontaneously. The model leads to an interesting relation for the charged lept…
We investigate neutrino mass matrix phenomenology involving scaling ansatz and texture zeros adhering inverse seesaw mechanism. It is seen that four is the maximum number of zeros in $m_D$ and $μ$ to obtain viable phenomenology. Depending upon the generic nature of the effective neutrino mass matrices we classify all the emerged matrices in four categories. One of them is ruled out phenomenologically due to inappropriate value of reactor mixing angle after breaking of the scaling ansatz. The mass ordering is inverted in all cases. One of the distinguishable feature of all these categories is t…
Ultraviolet Flavor Transmission to T-Violating Neutrino Oscillation Observables in a Seesaw Framework with Sterile Mixing and Planck-Suppressed Corrections
Department of Physics, Kirori Mal College, University of Delhi（德里大学科里尔马尔学院物理系）；Department of Physics, Chaudhary Charan Singh University（乔杜里·查兰·辛格大学物理系）
We consider the scenario in which neutrino data are explained by the interplay of type I and II seesaw terms in the Majorana neutrino mass matrix ${\cal M}_ν= {\cal M}_L - {\cal M}_D {\cal M}_R^{-1} {\cal M}_D^T$. We construct a predictive model with ${\cal M}_L$ proportional to the unit matrix, 3 diagonal texture zeros in ${\cal M}_R$, and ${\cal M}_D$ diagonal. We show how this pattern can be maintained by the non-Abelian discrete symmetry $A_4$, and discuss its phenomenological consequences. It turns out that the two types of seesaw give contributions of the same order to ${\cal M}_ν$. In t…
Motivated by recent results from neutrino experiments, we study the neutrino masses and mixing in the framework of a SUSY $SU(5)\times \mathbb{A}_{4} $ model. The hybrid of Type I and Type II seesaw mechanisms leads to the nonzero value of the reactor angle $θ_{13}\neq 0$ and to the recently disfavored maximal atmospheric angle $θ_{23} \neq45^{\circ}$ by the NOvA experiment. The phenomenological consequences of the model are studied for both normal and inverted mass hierarchies. The obtained ranges for the effective Majorana neutrino mass $m_{ββ}$, the electron neutrino mass $m_{ν_{e}}$, and t…
We propose a simple but suggestive seesaw model with two phenomenological conjectures: three heavy (right-handed) Majorana neutrinos are degenerate in mass in the symmetry limit and three light Majorana neutrinos have the tri-bimaximal mixing pattern $V^{}_0$. We show that a small mass splitting between the first generation and the other two generations of heavy Majorana neutrinos is responsible for the deviation of the solar neutrino mixing angle $θ^{}_{12}$ from its initial value $35.3^\circ$ given by $V^{}_0$, and the slight breaking of the mass degeneracy between the second and third gener…
