Right-handed Majorana Neutrino Mass Research Articles

Towards a systematic study of non-thermal leptogenesis from inflaton decays

This paper investigates non-thermal leptogenesis from inflaton decays in the minimal extension of the canonical type-I seesaw model, where a complex singlet scalar ϕ is introduced to generate the Majorana masses of right-handed neutrinos (RHNs) and to play the role of inflaton. First, we systematically study non-thermal leptogenesis with the least model dependence. We give a general classification of the parameter space and find four characteristic limits by carefully examining the interplay between inflaton decay into RHNs and the decay of RHNs into the standard-model particles. Three of the four limits are truly non-thermal, with a final efficiency larger than that of thermal leptogenesis. Two analytic estimates for these three limits are provided with working conditions to examine the validity. In particular, we find that the strongly non-thermal RHNs scenario occupies a large parameter space, including the oscillation-preferred K range, and works well for a relatively-low reheating temperature TRH ≥ 103 GeV, extending the lower bound on the RHN mass to 2 × 107 GeV. The lepton flavor effects are discussed. Second, we demonstrate that such a unified picture for inflation, neutrino masses, and baryon number asymmetry can be realized by either a Coleman-Weinberg potential (for the real part of ϕ) or a natural inflation potential (for the imaginary part of ϕ). The allowed parameter ranges for successful inflation and non-thermal leptogenesis are much more constrained than those without inflationary observations. We find that non-thermal leptogenesis from inflaton decay offers a testable framework for the early Universe. It can be further tested with upcoming cosmological and neutrino data. The model-independent investigation of non-thermal leptogenesis should be useful in exploring this direction.

Three-loop inverse scotogenic seesaw models

We propose a class of models providing an explanation of the origin of light neutrino masses, the baryon asymmetry of the Universe via leptogenesis and offering viable dark matter candidates. In these models the Majorana masses of the active neutrino are generated by the inverse seesaw mechanism with the lepton number violating right-handed Majorana neutrino masses μ arising at three loops. The latter is ensured by the preserved discrete symmetries, which also guarantee the stability of the dark matter candidate. We focus on one of these models and perform a detailed analysis of the phenomenology of its leptonic sector. The model can successfully accommodate baryogenesis through leptogenesis in both weak and strong washout regimes. The lightest heavy fermion turns out to be a viable dark matter candidate, provided that the entries of the Majorana submatrix μ are in the keV to MeV range. The solutions are consistent with the experimental constraints, accommodating both mass orderings for active neutrinos, in particular charged-lepton flavor violating decays μ → eγ, μ → eee, and the electron-muon conversion processes get sizable rates within future sensitivity reach.

Neutrino phenomenology in a model with generalized CP symmetry within type-I seesaw framework

We investigate the consequences of generalized CP (GCP) symmetry within the context of the two Higgs doublet model (2HDM), specifically focusing on the lepton sector. Utilizing the type-I seesaw framework, we study an intriguing connection between the Dirac Yukawa couplings originating from both Higgs fields, leading to a reduction in the number of independent Yukawa couplings and simplifying the scalar and Yukawa sectors when compared to the general 2HDM. The constraints coming from CP symmetry of class three (CP3) results in two right-handed neutrinos having equal masses and leads to a diagonal right-handed Majorana neutrino mass matrix. Notably, CP symmetry experiences a soft breaking due to the phase associated with the vacuum expectation value of the second Higgs doublet. The model aligns well with observed charged lepton masses and neutrino oscillation data, explaining both masses and mixing angles, and yields distinct predictions for normal and inverted neutrino mass hierarchies. It features a novel interplay between atmospheric mixing angle θ23 and neutrino mass hierarchy: The angle θ23 is below maximal for the normal hierarchy and above maximal for inverted hierarchy. Another interesting feature of the model is inherent CP violation for the inverted hierarchy. Published by the American Physical Society 2024

Non-SUSY lepton flavor model with the three Higgs doublet model

Abstract We propose a simple non-supersymmetric lepton flavor model with A4 symmetry. The A4 group is a minimal one that includes triplet irreducible representation. We introduce three Higgs doublets, which are assigned as a triplet of the A4 symmetry. It is natural that there are three generations of the Higgs fields, as with the standard model fermions. We analyze the potential and find the vacuum expectation values for the local minimum. In the vacuum expectation values, we obtain the charged lepton, Dirac neutrino, and right-handed Majorana neutrino mass matrices. By using the type-I seesaw mechanism, we get the left-handed Majorana neutrino mass matrix. In the NuFIT 5.1 data, we predict the Dirac CP phase and the Majorana phases for the only inverted neutrino mass hierarchy. In particular, the Dirac CP phase and lepton mixing angle θ23 are strongly correlated. If θ23 is more precisely measured, the Dirac CP phase is more precisely predicted, and vice versa. We also predict the effective mass for neutrinoless double beta decay mee ≃ 47.1 [meV] and the lightest neutrino mass m3 ≃ 0.789–1.43 [meV]. This will be testable with our model in near-future neutrino experiments.

Gauged U(1)Lμ−Lτ symmetry and two-zero textures of inverse neutrino mass matrix in light of muon (g − 2)

In the framework of anomaly free [Formula: see text] model, singlet scalar field with nonzero [Formula: see text] charge gives rise to massive gauge boson [Formula: see text] through spontaneous symmetry breaking. [Formula: see text] leads to one loop contribution to the muon anomalous magnetic moment. These scalar fields may, also, appear in the structure of right-handed neutrino mass matrix, thus, connecting the possible explanation of muon [Formula: see text] and low-energy neutrino phenomenology through vevs associated with the scalar fields. In this work, we consider textures of inverse neutrino mass matrix [Formula: see text] wherein any two elements of the mass matrix are zero. In this ansatz, with Dirac neutrino mass matrix diagonal, the zero(s) of right-handed Majorana neutrino mass matrix correspond to zero(s) in the low-energy effective neutrino mass matrix (within Type-I seesaw). We have realized two such textures of [Formula: see text] accommodating the muon [Formula: see text] and low-energy neutrino phenomenology. The requirement of successful explanation of muon [Formula: see text], further, constrains the allowed parameter space of the model and results in sharp correlations amongst neutrino mixing angles and CP invariants. The model explains muon [Formula: see text] for [Formula: see text] in the range (0.035–0.100 GeV) and [Formula: see text] which is found to be consistent with constraints coming from the current experiments CCFR, COHERENT, BABAR while being within sensitivities of future experiments such as NA62 and NA64.

Broken scaling neutrino mass matrix and leptogenesis based on A4 modular invariance

In this work, we have proposed a modular A4 symmetric model of neutrino mass which, simultaneously, explains observed baryon asymmetry of the Universe (BAU). In minimal extension of the standard model (SM) with two right-handed neutrinos we work in a supersymmetric framework. At Type-I seesaw level, the model predicts scaling in the neutrino mass matrix. In order to have correct low energy phenomenology, we propose two possible scenarios of scale-breaking in the neutrino mass matrix emanating from Type-I seesaw. Scenario-1 is based on the dimension-5 Weinberg operator whereas scenario-2 implements Type-II seesaw via scalar triplet Higgs superfields (∆, overline{Delta } ). Interestingly, the breaking patterns in both, otherwise dynamically different scenarios, are similar which can be attributed to the same charge assignments of superfields (∆, overline{Delta } ) and the Higgs superfield Hu under modular A4 symmetry. The breaking is found to be proportional to the Yukawa coupling of modular weight 10 ( {Y}_{1,1prime}^{10} ). We, further, investigates the predictions of the model under scenario-2 (Type-I+II) for neutrino mass, mixings and matter-antimatter asymmetry of the Universe. The model predicts normal hierarchical neutrino masses and provide a robust range (0.05 − 0.08)eV for sum of neutrino masses (Σmi). Lepton number violating 0νββ decay amplitude (Mee) is obtained to lie in the range (0.04 − 0.06)eV. Future 0νββ decay experiments such as NEXT and nEXO shall pose crucial test for the model. Both CP conserving and CP violating solutions are allowed in the model. Interesting correlations are obtained, specially, between Yukawa couplings of modular weight 2 and complex modulus τ. Contrary to {Y}_2^2 and {Y}_3^2 , the Yukawa coupling {Y}_1^2 is found to be insensitive to τ and thus to CP violation because complex modulus τ is the only source of CP violation in the model. We, also, investigate the prediction of the model for BAU. The model exhibit consistent explanation of BAU for right-handed Majorana neutrino mass scale in the range ((1 − 5) × 1013) GeV.

What if a specific neutrinoless double beta decay is absent?

Abstract We consider the seesaw model with two right-handed neutrinos, $N_1$ and $N_2$, the masses of which are hierarchical, and investigate their contribution to the neutrinoless double beta ($0 \nu \beta \beta$) decay. Although the lepton number is broken by the Majorana masses of right-handed neutrinos, such decay processes can be absent in some cases. We present a possibility where the lighter $N_1$ gives a destructive contribution to the decay of active neutrinos by choosing the specific mixing elements of $N_1$, while $N_2$ is sufficiently heavy not to contribute to the $0 \nu \beta \beta$ decay. In this case the mixing elements of $N_1$ in the charged current interaction are determined by its mass and the Majorana phase of active neutrinos. We then study the impacts of such a possibility on the direct search for $N_1$. In addition, we discuss the consequence of the case when the $0 \nu \beta \beta$ decay in one specific nucleus is absent.

Lepton flavor model with modular A4 symmetry in large volume limit

We consider the modular symmetry associated with the compactification of extra dimensions as the flavor symmetry on lepton sector. Especially, we propose a model based on the modular A4 symmetry with three right-handed neutrinos and a gauge singlet Higgs, which works well in the so-called large volume limit of the extra dimensions, i.e., Imτ→∞ for a modulus τ. The right-handed neutrinos are introduced to realize the seesaw mechanism for tiny neutrino masses observed in oscillation experiments. The vacuum expectation value of the singlet Higgs gives the Majorana masses for right-handed neutrinos and the μ-term for Higgs fields. The model can explain the observed masses and mixing angles of neutrinos successfully. We find that one of the mixing angles should be in the range sin2⁡θ23≥0.58. Importantly, the CP violating phases of neutrinos are predicted in the two restricted regions. One is that the Dirac phase is δCP≃−0.5π and the Majorana phases are α21≃0 and α31≃π. The other is δCP≃+0.5π, α21≃2π and α31≃π. The effective neutrino mass in the neutrinoless double beta decay is found to be meff=0.037–0.047 eV. These predictions will be tested in the future neutrino experiments.

TeV-scale resonant leptogenesis with new scaling ansatz on neutrino Dirac mass matrix from A4 flavor symmetry

We propose a new scaling ansatz in the neutrino Dirac mass matrix to explain the low energy neutrino oscillations data, baryon number asymmetry and neutrinoless double beta decay. In this work, a full reconstruction of the neutrino Dirac mass matrix has been realized from the low energy neutrino oscillations data based on type-I seesaw mechanism. A concrete model based on [Formula: see text] flavor symmetry has been considered to generate such a neutrino Dirac mass matrix and imposes a relation between the two scaling factors. In this model, the right-handed Heavy Majorana neutrino masses are quasi-degenerate at TeV mass scales. Extensive numerical analysis studies have been carried out to constrain the parameter space of the model from the low energy neutrino oscillations data. It has been found that the parameter space of the Dirac mass matrix elements lies near or below the MeV region and the scaling factor [Formula: see text] has to be less than 10. Furthermore, we have examined the possibility for simultaneous explanation of both neutrino oscillations data and the observed baryon number asymmetry in the Universe. Such an analysis gives further restrictions on the parameter space of the model, thereby explaining the correct neutrino data as well as the baryon number asymmetry via a resonant leptogenesis scenario. Finally, we show that the allowed space for the effective Majorana neutrino mass [Formula: see text] is also constrained in order to account for the observed baryon asymmetry.

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.

Alternative renormalizable SO(10) GUTs and data fitting

The alternative renormalizable minimal SO(10) model is composed of the Yukawa couplings with 10⊕120 Higgs fields, whereas the right-handed (RH) neutrino Majorana masses are generated via the Witten mechanism. The gauge coupling unification is achieved together with a unique pattern of the fermion masses and mixing at the grand unification scale due to additional contributions of vector-like quarks to the standard model renormalization group equations. We perform the fitting of the model to the experimental data of charged fermion masses and the CKM matrix. The best fit point is obtained with large pulls for mc, ms, mb, and mτ. For the modifications to the minimal model by adding either 10′ or 120′, a large deviation for the tau mass rules out all these models. In the case with the bottom and vector-like quark mixing, the mass matrices are well fitted the charged fermions but the bound on the light neutrino mass scale excludes this scenario. To ameliorate this deficit, we consider the two-step symmetry breaking scenario, SO(10)→SU(5)→SU(3)C×SU(2)L×U(1)Y, with the SO(10) breaking at the Planck scale leading to the radiatively generated RH neutrino Majorana masses being at the ordinary seesaw scale. For this case, we find the best fit point with χ2=7.8 consistent with experimental results including the neutrino sector. The largest deviation is 2.3σ corresponding to the strange quark mass. Hence, a more precise determination of the strange quark mass can test this model. For the best fit point, we find the effective Majorana neutrino mass of mββ=0.22 meV and the sum of light neutrino masses as Σ=0.078 eV, which are consistent with the current constraints from the search for the neutrinoless double beta decay and the CMB anisotropy measurement.

Gravitational waves from the minimal gauged U(1)B−L model

An additional $U(1)$ gauge interaction is one of promising extensions of the standard model of particle physics. Among others, the $U(1)_{B-L}$ gauge symmetry is particularly interesting because it addresses the origin of Majorana masses of right-handed neutrinos, which naturally leads to tiny light neutrino masses through the seesaw mechanism. We show that, based on the minimal $U(1)_{B-L}$ model, the symmetry breaking of the extra $U(1)$ gauge symmetry with its minimal Higgs sector in the early Universe can exhibit the first-order phase transition and hence generate a large enough amplitude of stochastic gravitational wave radiation which is detectable in future experiments.

Ameliorating the popular lepton mixings with A4 symmetry: A seesaw model for realistic neutrino masses and mixing

A model for neutrino masses and mixing is devised appointing the see-saw mechanism. The proffered model is fabricated with a combination of Type -I and Type-II see-saw contributions of which the latter dominates. The scalars and the leptons in the model are assigned $A4$ charges conducive to obtain the mass matrices viable for the scheme. The Type -II see-saw mass matrix accommodates atmospheric mass splitting and maximal mixing in the atmospheric sector ($\theta_{23}=\pi/4$). It is characterized by vanishing solar mass splitting and $\theta_{13}$ whereas the third neutrino mixing angle is free to acquire any value of $\theta_{12}^0$. Particular alternatives of $\theta_{12}^0$ corresponding to the popular lepton mixings viz. $\theta_{12}^0=35.3^\circ$ (tribimaximal), $45.0^\circ$ (bimaximal), $31.7^\circ$ (golden ratio) are accounted for. Another choice of $\theta_{12}^0=0^\circ$ (no solar mixing) is reckoned. The subdominant Type-I see-saw constituent of the model propels all the neutrino oscillation parameters into the ranges allowed by the data which in its turn get interrelated owing to their common origin. This makes the model testable in the light of future experimental data. As an example, $\theta_{23}$ emerges in the first (second) octant for normal (inverted) ordering. CP-violation is governed by phases present in the right-handed Majorana neutrino mass matrix, $M_{\nu R}$. Only normal ordering is allowed if these phases are absent. If $M_{\nu R}$ is complex the Dirac CP-violating phase $\delta$, is capable of being large, i.e., $\sim \pm \pi/2$, and inverted ordering of neutrino masses is also permitted. T2K and NOVA preliminary data favouring normal ordering and $\delta \sim -\pi/2$ predicts lightest neutrino mass to be 0.05 eV or more within the framework of this model.

Alternative renormalizable minimal SO(10) GUT and seesaw scale

Alternative renormalizable minimal non-SUSY SO(10) GUT model is proposed. Instead of a 126-dimensional Higgs field, a 120-dimensional Higgs filed is introduced in addition to a 10-dimensional Higgs field and plays a crucial role to reproduce the realistic charged fermion mass matrices. With contributions of 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 [Formula: see text] Higgs fields, while supplemented with a low scale seesaw mechanism due to the 2-loop induced right-handed Majorana neutrino mass.

Analysis of the right-handed Majorana neutrino mass in an SU(4)×SU(2)L×SU(2)R Pati-Salam model with democratic texture

In this paper, we attempt to build an unified model with democratic texture, that have some unification between $Y_{\nu}$ and $Y_{u}$. Since the $S_{3L} \times S_{3R}$ flavor symmetry is chiral, the unified gauge group is assumed to be Pati-Salam type $SU(4)_{c} \times SU(2)_{L} \times SU(2)_{R}$. The flavor symmetry breaking scheme is considered to be $S_{3L} \times S_{3R} \to S_{2L} \times S_{2R} \to 0$. In this picture, the four-zero texture is desirable for realistic mass and mixings. This texture is realized by a specific representation for the second breaking of the $S_{3L} \times S_{3R}$ flavor symmetry. Assuming only renormalizable Yukawa interactions, type-I seesaw mechanism, and neglecting $CP$ phases for simplicity, the right-handed neutrino mass matrix $M_{R}$ can be reconstructed from low energy input values. Numerical analysis shows that the texture of $M_{R}$ basically behaves like the "waterfall texture". Since $M_{R}$ tends to be the "cascade texture" in the democratic texture approach, a model with type-I seesaw and up-type Yukawa unification $Y_{\nu} \simeq Y_{u}$ basically requires fine-tunings between parameters. Therefore, it seems to be more realistic to consider universal waterfall textures for both $Y_{f}$ and $M_{R}$, e.g., by the radiative mass generation or the Froggatt--Nielsen mechanism. Moreover, analysis of eigenvalues shows that the lightest mass eigenvalue $M_{R1}$ is too light to achieve successful thermal leptogenesis. Although the resonant leptogenesis might be possible, it also requires fine-tunings of parameters.

Neutrino mass model with S3 symmetry and seesaw interplay

We develop a see-saw model for neutrino masses and mixing with an S3\times Z3 symmetry. It involves an interplay of Type-I and Type-II see-saw contributions of which the former is subdominant. The S3 \times Z3 quantum numbers of the fermion and scalar fields are chosen such that the Type-II see-saw generates a mass matrix which incorporates the atmospheric mass splitting and sets \theta_{23} = \pi/4. The solar splitting and \theta_{13} are absent, while the third mixing angle can achieve any value, \theta_{12}^0. Specific choices of \theta_{12}^0 are of interest, e.g., 35.3^\circ (tribimaximal), 45.0^\circ (bimaximal), 31.7^\circ (golden ratio), and 0^\circ (no solar mixing). The role of the Type-I see-saw is to nudge all the above into the range indicated by the data. The model results in novel interrelationships between these quantities due to their common origin, making it readily falsifiable. For example, normal (inverted) ordering is associated with \theta_{23} in the first (second) octant. CP-violation is controlled by phases in the right-handed neutrino Majorana mass matrix, M_{\nu R}. In their absence, only normal ordering is admissible. When M_{\nu R} is complex the Dirac CP-phase, \delta, can be large, i.e., \sim \pm \pi/2, and inverted ordering is also allowed. The preliminary results from T2K and NOVA which favour normal ordering and \delta \sim -\pi/2 are indicative, in this model, of a lightest neutrino mass of 0.05 eV or more.

Edge of a cliff

We discuss the neutrino flavor structures in the Occam's razor approach for the Dirac neutrino mass matrices. We assume that the charged lepton mass matrix takes a diagonal base, while the right-handed Majorana neutrino mass matrix is also diagonal and we consider nine patterns of the four zero textures for the Dirac neutrinos mass matrices. We numerically analyze the left-handed Majorana neutrino mass matrices for nine patterns of the Dirac neutrino mass matrices and we found two interesting patterns where both normal and inverted neutrino mass hierarchies can be realized. We also found if the neutrino mass is normal hierarchy, this scenario will be likely to be excluded by the measurements of the Dirac CP violating phase in the T2K and NO$\nu $A neutrino experiments, for instance. On the other hand, if the neutrino mass is inverted hierarchy, this scenario will be also likely to be excluded by the measurements of neutrinoless double beta decay experiments, e.g., KamLAND-Zen experiment.

Occam’s razor in lepton mass matrices: The sign of the universe’s baryon asymmetry

We discuss the neutrino mass matrix based on the Occam's Razor approach in the framework of the seesaw mechanism. We impose four zeros in the Dirac neutrino mass matrix, which give the minimum number of parameters needed for the observed neutrino masses and lepton mixing angles, while the charged lepton mass matrix and the right-handed Majorana neutrino mass matrix are taken to be real diagonal ones. The low-energy neutrino mass matrix has only seven physical parameters. We show successful predictions for the mixing angle $\theta_{13}$ and the CP violating phase $\delta_{CP}$ with the normal mass hierarchy of neutrinos by using the experimental data on the neutrino mass squared differences, the mixing angles $\theta_{12}$ and $\theta_{23}$. The most favored region of $\sin\theta_{13}$ is around $0.13\sim 0.15$, which is completely consistent with the observed value. The CP violating phase $\delta_{CP}$ is favored to be close to $\pm \pi/2$. We also discuss the Majorana phases as well as the effective neutrino mass for the neutrinoless double-beta decay $m_{ee}$, which is around $7\sim 8$ meV. It is extremely remarkable that we can perform a "complete experiment" to determine the low-energy neutrino mass matrix, since we have only seven physical parameters in the neutrino mass matrix. In particular, two CP violating phases in the neutrino mass matrix are directly given by two CP violating phases at high energy. Thus, assuming the leptogenesis we can determine the sign of the cosmic baryon in the universe from the low-energy experiments for the neutrino mass matrix.

Neutrino seesaw mechanism with texture zeros

In the context of the Type I seesaw mechanism, we carry out a systematic study of the constraints that result from zeros in both the Dirac and right-handed Majorana neutrino mass matrices. We find that most constraints can be expressed in the standard form with one or two element/cofactor zeros alone, while there are 9 classes of nonstandard constraints. We show that all the constraints are stable under one-loop renormalization group running from the lightest right-handed neutrino mass scale to the electroweak scale. We study the predictions of the nonstandard constraints for the lightest neutrino mass, Dirac CP phase and neutrinoless double beta decay.

Contribution of right-handed neutrinos and standard fermions to W± and Z masses

We present expressions of the Pagels–Stokar (PS) type for the masses of the [Formula: see text] and Z bosons in terms of the quark and lepton self-energies. By introducing a genuine new term in the gauge boson-fermion–anti-fermion vertex we manage to accomplish three main achievements: First, we show that the similar results existing in literature lead, in general, to a nonsymmetric gauge boson mass matrix and we fix this flaw. Second, we consider the case of any number of fermion generations with general mixing. Third, we include in our analysis also an arbitrary number of right-handed neutrinos, together with the left-handed and right-handed neutrino Majorana masses (self-energies). On top of that, we give also a correction to the original PS formula for the pion decay constant in QCD.