Light Neutrino Mass Matrix Research Articles

Prediction of the non-SUSY AdS conjecture on the lightest neutrino mass revisited

We study the constraint of the nonsupersymmetric (non-SUSY) anti–de Sitter (AdS) conjecture on the three-dimensional vacua obtained from the compactification of the Standard Model coupled to Einstein gravity on a circle where the three-dimensional components of the four-dimensional metric are general functions of both noncompact and compact coordinates. We find from studying the wave function profile of the three-dimensional metric in the compactified dimension that the radius of the compactified dimension must be quantized. Consequently, the three-dimensional vacua are constrained by not only the non-SUSY AdS conjecture but also the quantization rule of the circle radius, leading to both upper and lower bounds for the mass of the lightest neutrino as 2≤mν/Λ4<3, where Λ4≃5.06×10−84 GeV2 is the observed cosmological constant. This means that the lightest neutrino should have a mass around 10−32 eV or it would be approximately massless. With this prediction, we reconstruct the light neutrino mass matrix that is fixed by the neutrino oscillation data and in terms of three new mixing angles and six new phases for both the normal ordering and inverted ordering. In the situation where the light neutrino mass matrix is Hermitian, we calculate its numerical value in the 3σ range. Published by the American Physical Society 2024

Neutrino model with broken [formula omitted] -[formula omitted] symmetry and unflavored leptogenesis with dihedral flavor symmetry

We propose a new neutrino flavor model based on a D4×U(1) flavor symmetry providing predictions for neutrino masses and mixing along with a successful generation of the observed Baryon Asymmetry of the Universe (BAU). After the spontaneous breaking of the flavor symmetry, the type I seesaw mechanism leads to a light neutrino mass matrix with broken μ−τ symmetry. By performing a numerical analysis, we find that the model favors a normal mass hierarchy with the lightest neutrino mass lies in the range m1∈[2.516,21.351] meV. The phenomenological implications of the neutrino sector are explored in detail and the results are discussed. Moreover, the generation of BAU is addressed via the leptogenesis mechanism from the decay of three right-handed neutrinos Ni. Through analytical and numerical analysis of the baryon asymmetry parameter YB, a successful unflavored leptogenesis takes place within the allowed parameter space obtained from neutrino phenomenology. We also examine interesting correlations between YB and low energy observables and provide a comprehensive discussion of the results.

Common origin of θ13 and dark matter within the flavor symmetric scoto-seesaw framework

To understand the observed pattern of neutrino masses and mixing as well as to account for the dark matter we propose a hybrid scoto-seesaw model based on the A4 discrete flavor symmetry. In this setup, including at least two heavy right-handed neutrinos is essential to employ the discrete flavor symmetry that mimics once popular tribimaximal neutrino mixing at the leading order via type-I seesaw. The scotogenic contribution then acts as a critical deviation to reproduce the observed value of the reactor mixing angle θ13 (within the trimaximal mixing scheme) and to accommodate potential dark matter candidates, pointing towards a common origin of θ13 and dark matter. The model predicts the atmospheric angle to be in the upper octant, excludes some regions on the Dirac CP phase, and restricts the Majorana phases too. Further, normal and inverted mass hierarchies can be distinguished for specific values of the relative phases associated with the complex light neutrino mass matrix. Owing to the considered flavor symmetry, contributions coming from the scotogenic mechanism towards the lepton flavor violating decays such as μ → eγ, τ → eγ vanish, and a lower limit on the second right-handed neutrino mass can be obtained. Prediction for the effective mass parameter appearing in the neutrinoless double beta decay falls within the sensitivity of future experiments such as LEGEND-1k and nEXO.

Neutrino mass and charged lepton flavor violation in an extended left-right symmetric model

We consider an U(1)Lμ−Lτ extended left-right symmetric gauge theory where the neutrino masses are generated through inverse seesaw mechanism. In this model the muon (g−2) anomaly is accounted for by the mediation of Zμτ, the gauge boson of U(1)Lμ−Lτ symmetry. The symmetries of the model require the light neutrino mass matrix to have a particular two-zero texture, which leads to non-trivial constraints in the minimum neutrino mass. In addition, the model predicts observable charged lepton flavor violation in μ−τ sector.

Flavour and CP symmetries in the inverse seesaw

We consider an inverse seesaw mechanism of neutrino mass generation in which the Standard Model is extended by 3+3 (heavy) sterile states, and endowed with a flavour symmetry G_f, G_f=Delta (3 , n^2) or G_f=Delta (6 , n^2), and a CP symmetry. These symmetries are broken in a peculiar way, so that in the charged lepton sector a residual symmetry G_ell is preserved, while the neutral fermion sector remains invariant under the residual symmetry G_nu =Z_2 times CP. We study the concrete setup, where the Majorana mass term for three of the sterile states conserves G_nu , while the remaining mass terms (i.e. couplings of left-handed leptons and heavy sterile states, as well as the Dirac-type couplings among the latter) do not break the flavour or CP symmetry. We perform a comprehensive analysis of lepton mixing for different classes of residual symmetries, giving examples for each of these, and study in detail the impact of the additional sterile states on the predictions for lepton mixing. We further confront our results with those obtained in the model-independent scenario, in which the light neutrino mass matrix leaves the residual symmetry G_nu intact. We consider the phenomenological impact of the inverse seesaw mechanism endowed with flavour and CP symmetries, in particular concerning effects of non-unitarity of the lepton mixing matrix (which strongly constrain the parameter space of the scenario), prospects for neutrinoless double beta decay and for charged lepton flavour violating processes.

A generalization of the Scotogenic model

The Scotogenic model is a radiative neutrino mass model able to induce Majorana neutrino masses at the 1-loop level and simultaneously include a dark matter candidate. In this work, we generalize the original Scotogenic model to arbitrary numbers of generations of the Scotogenic states. After that, we present the light neutrino mass matrix, with some details of its derivation, and provide a useful approximate expression as well. Finally, we numerically solve the Renormalization Group Equations to explore the high-energy behavior of the model. 1

Phenomenological study of type II seesaw with Δ(27) symmetry

We discuss the phenomenology of type-II seesaw by extending the standard model with additional Higgs doublets, scalar triplets as well as a scalar singlet invoked with discrete flavor symmetry Δ(27), for the explanation of non-zero neutrino masses and mixing, matter–antimatter asymmetry, and lepton flavor violation (LFV). The light neutrino masses can be obtained via type-II seesaw mechanism by transforming scalar triplets as 3 and scalar doublets as various singlet representations like 1 1 , 1 2 , 1 3 along with scalar singlet as 1 1 under Δ(27) symmetry. With the implementation of this discrete flavor symmetry Δ(27), we get simpler structure for light neutrino mass matrix, which helps in analyzing neutrino phenomenology analytically as well as numerically. We further demonstrate the detailed numerical analysis by scanning the input model parameters in agreement with neutrino oscillation data like non-zero reactor mixing angle (θ 13), CP-violating phase (δ CP), the sum of the light neutrino masses, two mass squared differences, and its implication to neutrino-less double beta decay. The model also explains the matter–antimatter asymmetry of the Universe through resonant leptogenesis with the decay of TeV scale scalar triplets and variation of CP-asymmetry with input model parameters. Finally, we comment on the implication to LFV decays like μ → eγ, μ → 3e processes via the mediation of these TeV scale scalar triplets. We have studied collider physics briefly.

Survey of texture zeros with light Dirac neutrinos

We classify all possible texture zeros in a light neutrino mass matrix in a diagonal charged lepton basis by considering the Dirac nature of light neutrinos. For the Hermitian nature of neutrino mass matrix, the number of possible texture zeros remain the same as Majorana texture zeros, but with less free parameters due to the absence of additional Majorana CP phases. Relaxing the Hermitian nature of the neutrino mass matrix leads to many more possibilities and freedom due to additional CP phases, mixing angles not constrained by neutrino data. While we find only a very few of the one-zero and two-zero textures in the Hermitian case to be allowed, in the non-Hermitian case some textures even with four zeros are allowed. While most of the one-zero, two-zero and three-zero textures in this case are allowed, four-zero textures are tightly constrained with only six allowed out of 126 possibilities. The allowed textures also give interesting correlations between light neutrino parameters with sharp distinctions between normal and inverted mass ordering. Many of these allowed textures also saturate the Planck 2018 upper bound on the sum of absolute neutrino masses.

Radiative seesaw corrections and charged-lepton decays in a model with soft flavour violation

We consider the one-loop radiative corrections to the light-neutrino mass matrix and their consequences for the predicted branching ratios of the five lepton-flavour-violating decays {mathrm{ell}}_1^{-}to {mathrm{ell}}_2^{-}{mathrm{ell}}_3^{+}{mathrm{ell}}_3^{-} in a two-Higgs-doublet model furnished with the type-I seesaw mechanism and soft lepton-flavour violation. We find that the radiative corrections are very significant; they may alter the predicted branching ratios by several orders of magnitude and, in particular, they may help explain why BR (μ− → e−e+e−) is strongly suppressed relative to the branching ratios of the decays of the τ−. We conclude that, in any serious numerical assessment of the predictions of this model, it is absolutely necessary to take into account the one-loop radiative corrections to the light-neutrino mass matrix.

Revisiting Majorana neutrino textures in the light of dark LMA

We study the possibility of texture zeros in Majorana light neutrino mass matrix in the light of dark large mixing angle (DLMA) solution to solar neutrino problem where solar mixing angle (sin2 θ 12 ≃ 0.7) lies in the second octant instead of first octant in standard large mixing angle (LMA) scenario (sin2 θ 12 ≃ 0.3). In three neutrino scenario, we find that LMA and DLMA solutions lead to different set of allowed and disallowed textures with one and two zeros. While being consistent with existing bounds from neutrino oscillation data, neutrinoless double beta decay and cosmology these allowed textures also lead to interesting correlations among light neutrino parameters which can distinguish LMA from DLMA solution. We also check the implications for texture zeros in 3 + 1 neutrino scenario using both LMA and DLMA solutions. While LMA and DLMA solutions do not play decisive role in ruling out texture zeros in this case, they do give rise to distinct predictions and correlations between light neutrino parameters.

Generalizing the Scotogenic model

The Scotogenic model is an economical setup that induces Majorana neutrino masses at the 1-loop level and includes a dark matter candidate. We discuss a generalization of the original Scotogenic model with arbitrary numbers of generations of singlet fermion and inert doublet scalar fields. First, the full form of the light neutrino mass matrix is presented, with some comments on its derivation and with special attention to some particular cases. The behavior of the theory at high energies is explored by solving the Renormalization Group Equations.

Phenomenological study of texture zeros of neutrino mass matrix in minimal left-right symmetric model

We studied the phenomenological implications of texture zeros in the neutrino mass matrix of the minimal left-right symmetric model (LRSM). Since the possibility of maximum zeros reduces the maximum number of free parameters of the model making it more predictive, we considered only those cases with maximum possible texture zeros in light neutrino mass matrix Mv , Dirac neutrino mass matrix MD and heavy right-handed (RH) neutrino mass matrix MRR . We then computed the correlations among the different light neutrino parameters and then the new physics contributions to neutrinoless double beta decay(NDBD) for the different texture zero cases. We find that for RH neutrino masses above 1 GeV, the new physics contributions to NDBD can saturate the corresponding experimental bound.

Modular S4 and A4 symmetries and their fixed points: new predictive examples of lepton mixing

In the modular symmetry approach to neutrino models, the flavour symmetry emerges as a finite subgroup ΓN of the modular symmetry, broken by the vacuum expec- tation value (VEV) of a modulus field τ. If the VEV of the modulus τ takes some special value, a residual subgroup of ΓN would be preserved. We derive the fixed points τS = i, τST = (−1 + i sqrt{3} )/2, τTS = (1 + i sqrt{3} )/2, τT = i∞ in the fundamental domain which are in-variant under the modular transformations indicated. We then generalise these fixed points to τf = γτS, γτST, γτTS and γτT in the upper half complex plane, and show that it is suffi-cient to consider γ ∈ ΓN. Focussing on level N = 4, corresponding to the flavour group S4, we consider all the resulting triplet modular forms at these fixed points up to weight 6. We then apply the results to lepton mixing, with different residual subgroups in the charged lepton sector and each of the right-handed neutrinos sectors. In the minimal case of two right-handed neutrinos, we find three phenomenologically viable cases in which the light neutrino mass matrix only depends on three free parameters, and the lepton mixing takes the trimaximal TM1 pattern for two examples. One of these cases corresponds to a new Littlest Modular Seesaw based on CSD(n) with n = 1 + sqrt{6} ≈ 3.45, intermediate between CSD(3) and CSD(4). Finally, we generalize the results to examples with three right-handed neutrinos, also considering the level N = 3 case, corresponding to A4 flavour symmetry.

Seesaw neutrinos with one right-handed singlet field and a second Higgs doublet

We study parameters of an extension of the Standard Model. The neutrino sector is enlarged by one right-handed singlet field, allowing for the seesaw mechanism type-I, and the Higgs sector contains one additional doublet, which contributes to light neutrino masses through one-loop radiative corrections. Employing an approximation for the effective light neutrino mass matrix we express the masses of the light neutrinos analytically, allowing us to parameterize the Yukawa couplings to neutrinos by the experimental measurements on the neutrino sector and only two free parameters. We focus on a CP-conserving Higgs potential for which we present the allowed ranges of the input parameters and a statistical overview over the possible values of the Yukawa couplings.

Long-lived TeV-scale right-handed neutrino production at the LHC in gauged U(1)X model

A gauged U(1)X extension of the Standard Model is a simple and consistent framework to naturally incorporate three right-handed neutrinos (RHNs) for generating the observed light neutrino masses and mixing by the type-I seesaw mechanism. We examine the collider testability of the U(1)X model, both in its minimal form with the conventional charges, as well as with an alternative charge assignment, via the resonant production of the U(1)X gauge boson (Z′) and its subsequent decay into a pair of RHNs. We first derive an updated upper limit on the new gauge coupling gX as a function of the Z′-boson mass from the latest LHC dilepton searches. Then we identify the maximum possible cross section for the RHN pair-production under these constraints. Finally, we investigate the possibility of having one of the RHNs long-lived, even for a TeV-scale mass. Employing the general parametrization for the light neutrino mass matrix to reproduce the observed neutrino oscillation data, we perform a parameter scan and find a simple formula for the maximum RHN lifetime as a function of the lightest neutrino mass eigenvalue (mlightest). We find that for mlightest≲10−5 eV, one of the RHNs in the minimal U(1)X scenario can be long-lived with a displaced-vertex signature which can be searched for at the LHC and/or with a dedicated long-lived particle detector, such as MATHUSLA. In other words, once a long-lived RHN is observed, we can set an upper bound on the lightest neutrino mass in this model.

Leptogenesis after superconformal subcritical hybrid inflation

We consider an extended version of superconformal subcritical hybrid inflation model by introducing three right-handed neutrinos that have the Majorana mass terms. In the model one of the right-handed sneutrinos plays a role of the inflaton field, and it decays to reheat the universe after inflation. The vacuum expectation value for the waterfall field gives an unconventional pattern of the light neutrino mass matrix, and the neutrino Yukawa couplings that determine the reheating temperature are not constrained by the neutrino oscillation data. Consequently thermal leptogenesis or sneutrino leptogenesis is realized.

Flavor from the double tetrahedral group without supersymmetry: Flavorful axions and neutrinos

We extend the work of Carone, Chaurasia and Vasquez on non-supersymmetric models of flavor based on the double tetrahedral group. Three issues are addressed: (1) the sector of flavor-symmetry-breaking fields is simplified and their potential studied explicitly, (2) a flavorful axion is introduced to solve the strong CP problem and (3) the model is extended to include the neutrino sector. We show how the model can accommodate the strong hierarchies manifest in the charged fermion Yukawa matrices, while predicting a qualitatively different form for the light neutrino mass matrix that is consistent with observed neutrino mass squared differences and mixing angles.

Phenomenological study of texture zeros in lepton mass matrices of minimal left-right symmetric model

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 Mν, Dirac neutrino mass matrix MD, heavy neutrino mass matrix MRR while keeping the determinant of MRR non-vanishing, in order to use the standard type I seesaw formula. The possibility of maximum zeros reduces the free parameters of the model making it more predictive. We then compute the new physics contributions to rare decay processes like neutrinoless double beta decay, charged lepton flavour violation. We find that even for a conservative lower limit on left-right symmetry scale corresponding to heavy charged gauge boson mass 4.5 TeV, in agreement with collider bounds, for right-handed neutrino masses above 1 GeV, the new physics contributions to these rare decay processes can saturate the corresponding experimental bound.

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.

Three-flavored nonresonant leptogenesis at intermediate scales

Leptogenesis can successfully explain the matter-antimatter asymmetry via out-of-equilibrium decays of heavy Majorana neutrinos in the early Universe. In this article, we focus on nonresonant thermal leptogenesis and the possibility of lowering its scale. In order to do so, we calculate the lepton asymmetry produced from the decays of one and two heavy Majorana neutrinos using three-flavored density matrix equations in an exhaustive exploration of the model parameter space. We find regions of the parameter space where thermal leptogenesis is viable at intermediate scales, $T\ensuremath{\sim}{10}^{6}\text{ }\text{ }\mathrm{GeV}$. However, the viability of thermal leptogenesis at such scales requires a certain degree of cancellation between the tree- and one-loop level contribution to the light neutrino mass matrix, and we quantify such fine-tuning.