type-II Seesaw Research Articles

A radiative type-II seesaw model with broken symmetry ansatz

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 ∼ 46.08°, θ 13 ∼ 8.69°. 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 data for a suitable choice of model parameters.

Low energy constraints from absolute neutrino mass observables and lepton flavor violation in left-right symmetric model

We have studied the correlations among the three absolute neutrino mass observables - the effective Majorana mass ($m_{ee}$) which can be obtained from neutrinoless double beta decay, the electron neutrino mass ($m_{\beta}$) which is measured in single beta decay experiments and the sum of the light neutrino masses ($\Sigma$) which is constrained from cosmological observations, in the context of minimal left-right symmetric model. Two phenomenologically interesting cases of type-I seesaw dominance as well as type-II seesaw dominance have been considered. We have taken into account the independent constraints coming from lepton flavor violation, single $\beta$ decay, cosmology and neutrinoless double beta decay and have determined the combined allowed parameter space that can be probed in the future experiments. We have also analyzed the correlations and tensions between the different mass variables. In addition, the constraints on the masses of the heavy particles coming from lepton flavor violation and the bounds on three absolute neutrino mass observables are also determined. We show that these constraints can rule out some of the parameter space which are not probed by the collider experiments.

Unification predictions with or without supersymmetry

Supersymmetric (SUSY) grand unified theories (GUTs) appear to be best motivated for understanding strong, weak and electromagnetic interactions of nature. We briefly review emergence of new formulas for running fermion masses valid in direct breaking of GUTs. High scale mixing unification of quark and neutrino mixings and existence of theorems on vanishing theoretical uncertainties in GUT predictions are discussed. D-Parity properties of SO(10) representations leading to large number of intermediate breaking models are pointed out. Unification predictions of SUSY SO(10) in the light of neutrino mass, lepton flavor violation, baryogenesis via leptogenesis within gravitino constraint, and proton decay are noted. We further discuss realisation of flavour unification and possibility of fitting all fermion masses through R-Parity and D-Parity conserving left-right symmetric intermediate breaking in SUSY SO(10)$\times S_4$. In the absence of SUSY two interesting possibilities of minimal grand desert modifications with only one intermediate mass scalar in each case and their applications to dark matter decay through type-I seesaw are briefly noted. Heavy scalar triplet decay leptogenesis through new ansatz for type-II seesaw dominance in non-SUSY SO(10), emergence of new CP asymmetry formulas and model capabilities to explain WIMP dark matter, vacuum stability of the scalar potential and experimentally observed limit on proton lifetime are briefly summarized.

Texture zeros flavor neutrino mass matrix and triplet Higgs models

One- and two-zero textures for the flavor neutrino mass matrix have been successful in explaining mixing in the neutrino sector. Conservatively, six cases of one-zero textures and seven cases of two-zero textures are compatible with observations. We show that one case may be the most natural in the one- and two-zero textures schemes if tiny neutrino masses are generated by the type-II seesaw mechanism in triplet Higgs models.

Purely triplet seesaw and leptogenesis within cosmological bound, dark matter, and vacuum stability

In a novel standard model extension it has been suggested that, even in the absence of right-handed neutrinos and type-I seesaw, purely triplet leptogenesis leading to baryon asymmetry of the universe can be realized by two heavy Higgs triplets which also provide type-II seesaw ansatz for neutrino masses. In this work we discuss this model predictions for hierarchical neutrino masses in concordance with recently determined cosmological bounds and oscillation data including θ23 in the second octant and large Dirac CP phases. We find that for both normal and inverted orderings, the model fits the oscillation data with the sum of the three neutrino masses consistent with current cosmological bounds determined from Planck satellite data. In addition, using this model ansatz for CP-asymmetry and solutions of Boltzmann equations, we also show how successful predictions of baryon asymmetry emerges in the cases of both unflavoured and two-flavoured leptogeneses. With additional Z2 discrete symmetry, a minimal extension of this model is further shown to predict a scalar singlet WIMP dark matter in agreement with direct and indirect observations which also resolves the issue of vacuum instability persisting in the original model. Although the combined constraints due to relic density and direct detection cross section allow this scalar singlet dark matter mass to be mξ=750 GeV, the additional vacuum stability constraint pushes this limiting value to mξ=1.3 TeV which is verifiable by ongoing experiments. We also discuss constraint on the model parameters for the radiative stability of the standard Higgs mass.

New mechanism for matter-antimatter asymmetry and connection with dark matter

We propose a new mechanism for generating matter-antimatter asymmetry via the interference of tree-level diagrams only, where the imaginary part of the Breit-Wigner propagator for an unstable mediator plays a crucial role. We first derive a general result that a nonzero $CP$-asymmetry can be generated via at least two sets of interfering tree-level diagrams involving either $2\rightarrow2$ or $1\rightarrow n$ (with $n\geq3$) processes. We illustrate this point in a simple TeV-scale extension of the Standard Model with an inert Higgs doublet and right-handed neutrinos, along with an electroweak-triplet scalar field, where small Majorana neutrino masses are generated via a combination of radiative type-I and tree-level type-II seesaw mechanisms. The imaginary part needed for the required $CP$-asymmetry comes from the trilinear coupling of the inert doublet with the triplet scalar, along with the width of the triplet scalar mediator. The real part of the neutral component of the inert doublet serves as a cold dark matter candidate. The evolutions of the dark matter relic density and the baryon asymmetry are intimately related in this scenario.

Type II seesaw models with modular A4 symmetry

We discuss type-II seesaw models adopting modular $A_4$ symmetry in supersymmetric framework. In our approach, the models are classified by the assignment of $A_4$ representations and modular weights for leptons and triplet Higgs fields. Then neutrino mass matrix is characterized by modulus $\tau$ and two free parameters. Carrying out numerical analysis, we find allowed parameter sets which can fit the neutrino oscillation data. For the allowed parameter sets, we obtain the predictions in neutrino sector such as CP violating phases and the lightest neutrino mass. Finally we also show the predictions for the branching ratios of doubly charged scalar boson focusing on the case where the doubly charged scalar boson dominantly decays into charged leptons.

Type-II neutrino seesaw mechanism extension of NMSSM from SUSY breaking mechanisms

We propose to accommodate economically the type-II neutrino seesaw mechanism in (G)NMSSM from GMSB and AMSB, respectively. The heavy triplets within neutrino seesaw mechanism are identified to be the messengers. Therefore, the mu -problem, the neutrino mass generation, LFV as well the soft SUSY breaking parameters can be economically combined in a non-trivial way. General features of such extensions are discussed. The type-II neutrino seesaw-specific interactions can give additional Yukawa deflection contributions to the soft SUSY breaking parameters of NMSSM, which are indispensable to realize successful EWSB and accommodate the 125 GeV Higgs. Relevant numerical results, including the constraints of dark matter and possible LFV processes l_irightarrow l_j gamma etc, are also given. We find that our economical type-II neutrino seesaw mechanism extension of NMSSM from AMSB or GMSB can lead to realistic low energy NMSSM spectrum, both admitting the 125 GeV Higgs as the lightest CP-even scalar. The possibility of the 125 GeV Higgs being the next-to-lightest CP-even scalar in GMSB-type scenario is ruled out by the constraints from EWSB, collider and precision measurements. The possibility of the 125 GeV Higgs being the next-to-lightest CP-even scalar in AMSB-type scenario is ruled out by dark matter direct detection experiments. Possible constraints from LFV processes l_irightarrow l_j gamma can give an upper bound for the messenger scale.

Dirac neutrinos from Peccei-Quinn symmetry: Two examples

We aim to explain the nature of neutrinos using Peccei-Quinn symmetry. We discuss two simple scenarios, one based on a type-II Dirac seesaw and the other in a one-loop neutrino mass generation, which solve the strong CP problem and naturally lead to Dirac neutrinos. In the first setup latest neutrino mass limit gives rise to axion which is in the reach of conventional searches. Moreover, we have both axion as well as WIMP dark mater for our second set up.

Magic neutrino mass model with broken μ − τ symmetry and leptogenesis

We investigate baryogenesis via leptogenesis in an A4 flavor model within the paradigm of type-I and II seesaw mechanism resulting in a magic neutrino mass matrix with broken μ − τ symmetry in a minimal scenario with two right-handed neutrinos (2RHN). Additional Z3 cyclic symmetry is employed to constrain the Yukawa structure of the model. The type-II seesaw terms play a crucial role in generating non-degenerate neutrino masses and non-zero θ13 and contribute to baryogenesis. In particular, after the spontaneous symmetry breaking, the Yukawa couplings and are responsible for the breaking of μ − τ symmetry. The effective Majorana neutrino mass is found to be well within the sensitivity reach of the 0νββ experiments, in particular, for inverted hierarchy. The model has an imperative implication for inverted hierarchy, for example, the non-observation of this process at nEXO will rule out IH. The predicted baryon asymmetry is in good agreement with the observed baryon asymmetry for NH whereas IH is disallowed at 2.5σ C.L.

Probing doubly and singly charged Higgs bosons at the pp collider HE-LHC

We analyse the signal sensitivity of multi-lepton final states at collider that can arise from doubly and singly charged Higgs decay in a type-II seesaw framework. We assume triplet vev to be very small and degenerate masses for both the charged Higgs states. The leptonic branching ratio of doubly and singly charged Higgs states have a large dependency on the neutrino oscillation parameters, lightest neutrino mass scale, as well as neutrino mass hierarchy. We explore this as well as the relation between the leptonic branching ratios of the singly and doubly charged Higgs states in detail. We evaluate the effect of these uncertainties on the production cross-section. Finally, we present a detailed analysis of multi-lepton final states for a future hadron collider HE-LHC, that can operate with center of mass energy $\sqrt{s}=27$ TeV.

Scalar triplet leptogenesis in the presence of right-handed neutrinos with S3 symmetry

Leptogenesis appears to be a viable alternative to account for the baryon asymmetry of the Universe through baryogenesis. In this context, we consider a scenario in which the standard model is extended with S3 and Z2 symmetry in addition to the two scalar triplets, two scalar doublets and three right-handed neutrinos. Presence of scalar triplets and right-handed neutrinos in the scenarios of both type-I and type-II seesaw frameworks provide a different leptogenesis option and can help us to understand the matter-antimatter asymmetry with simple S3 symmetry. We discuss the neutrino phenomenology and leptogenesis in both high (O(1010) GeV) and low energy scale (O(2) TeV) by constraining the Yukawa couplings. Moreover, we also consider the constraints on model parameters from neutrino oscillation data and leptogenesis to explain the rare lepton flavor violating decay and muon g-2 anomaly.

Connection between νn→ν¯n¯ reactions and n−n¯ oscillations via additional Higgs triplet bosons

In this work, we investigate the connection and compatibility between $\ensuremath{\nu}n\ensuremath{\rightarrow}\overline{\ensuremath{\nu}}\overline{n}$ reactions and $n\text{\ensuremath{-}}\overline{n}$ oscillations based on the $SU(3{)}_{c}\ifmmode\times\else\texttimes\fi{}SU(2{)}_{L}\ifmmode\times\else\texttimes\fi{}U(1)$ symmetry model with additional Higgs triplets. We explore the possibility that the scattering process $\ensuremath{\nu}n\ensuremath{\rightarrow}\overline{\ensuremath{\nu}}\overline{n}$ produced by low-energy solar neutrinos gives rise to an unavoidable background in the measurements of $n\text{\ensuremath{-}}\overline{n}$ oscillations. We focus on two different scenarios, depending on whether the ($B\ensuremath{-}L$) symmetry could be broken. We analyze the interplay of the various constraints on the two processes and their observable consequences. In the scenario where both ($B+L$) and ($B\ensuremath{-}L$) could be broken, we point out that if all the requirements, mainly arising from the type-II seesaw mechanism, are satisfied, the parameter space would be severely constrained. In this case, although the masses of the Higgs triplet bosons could be within the reach of a direct detection at the LHC or future high-energy experiments, the predicted $n\text{\ensuremath{-}}\overline{n}$ oscillation times would be completely beyond the detectable regions of the present experiments. In both scenarios, the present experiments are unable to distinguish a $\ensuremath{\nu}n\ensuremath{\rightarrow}\overline{\ensuremath{\nu}}\overline{n}$ reaction event from an $n\text{\ensuremath{-}}\overline{n}$ oscillation event within the accessible energy range. Nevertheless, if any of the two processes is detected, there could be signal associated with new physics beyond the Standard Model.

Double type II seesaw mechanism accompanied by Dirac fermionic dark matter

In the type-II seesaw mechanism, the neutrino mass generation could be tested experimentally if the Higgs triplet is at the TeV scale and has a small cubic coupling to the standard model Higgs doublet. We show such small triplet-doublet coupling and the cosmic baryon asymmetry can be simultaneously induced by an additional seesaw mechanism involving a $U(1)_{B-L}$ gauge symmetry. Meanwhile, three neutral fermions for cancelling the gauge anomalies can form a stable Dirac fermionic dark matter besides an acceptably massless fermion.

Triplet leptogenesis, type-II seesaw dominance, intrinsic dark matter, vacuum stability and proton decay in minimal SO(10) breakings

We implement type-II seesaw dominance for neutrino mass and baryogenesis through heavy scalar triplet leptogenesis in a class of minimal non-supersymmetric SO(10) models where matter parity as stabilising discrete symmetry as well as WIMP dark matter (DM) candidates are intrinsic predictions of the GUT symmetry. We also find modifications of relevant CP-asymmetry formulas in such models. Baryon asymmetry of the universe as solutions of Boltzmann equations is further shown to be realized for both normal and inverted mass orderings in concordance with cosmological bound and best fit values of the neutrino oscillation data including θ23 in the second octant and large values of leptonic Dirac CP-phases. Type-II seesaw dominance is at first successfully implemented in two cases of spontaneous SO(10) breakings through SU(5) route where the presence of only one non-standard Higgs scalar of intermediate mass ∼ 109−1010 GeV achieves unification. Lower values of the SU(5) unification scales ∼ 1015 GeV are predicted to bring proton lifetimes to the accessible ranges of Super-Kamiokande and Hyper-Kamiokande experiments. Our prediction of WIMP DM relic density in each model is due to a ∼ \U0001d4aa (1) TeV mass matter-parity odd real scalar singlet (⊂ 16H ⊂ SO(10)) verifiable by LUX and XENON1T experiments. This DM is also noted to resolve the vacuum stability issue of the standard scalar potential. When applied to the unification framework of M. Frigerio and T. Hambye, in addition to the minimal fermionic triplet DM solution of 2.7 TeV, our mechanism of type-II seesaw dominance and triplet leptogenesis is also found to make an alternative prediction of the triplet fermion plus the real scalar singlet DM near the TeV scale.

Baryon asymmetry from left-right phase transition

We extend the standard model fermions by a mirror copy to realize a left-right symmetry. During a strongly first order phase transition of the spontaneous left-right symmetry breaking, the CP-violating reflections of the mirror fermions off the mirror Higgs bubbles can generate a mirror lepton asymmetry and an equal mirror baryon asymmetry. We then can obtain an ordinary baryon asymmetry through the mirror fermion decays where a dark matter scalar plays an essential role. Benefitted from a parity symmetry for solving the strong CP problem, the cosmic baryon asymmetry can be well described by the ordinary lepton mass matrices up to an overall factor. In this scenario, the Dirac CP phase in the Majorana neutrino mass matrix can provide a unique source for the required CP violation. Furthermore, the Higgs triplet for type-II seesaw as well as the first generation of mirror charged fermions can be allowed at the TeV scale.

Associated production of SM Higgs with a photon in type-II seesaw models at the ILC

We consider the production of a single Standard Model (SM) Higgs boson (h^0) in association with a photon at the future Linear collider (LC) in the context of a type-II seesaw model. The type-II seesaw model extends the SM particle content by adding one triple Higgs where its Higgs coupling is a key parameter of the scalar potential triggering the electroweak symmetry-breaking mechanism in the SM. It is a well motivated model since it provides neutrino masses and mixing. The LC presents a particularly interesting possibility to probe Higgs couplings due to the clean beams in the initial state. We study the one loop processes e^+e^- rightarrow h^0gamma and e^-gamma rightarrow e^- h^0, we show that it is possible to correlate the total cross section predictions with the couplings h^0gamma gamma and h^0gamma Z which are sensitive to the presence of singly and doubly charged Higgs. For parameter points allowed by the current experimental constraints, our numerical results show that the effect of H^pm and H^{pm pm } can be as large as ± 25% with respect to the SM predictions. For both processes, we also present differential cross section for different center of mass energy.

Radiatively scotogenic type-II seesaw and a relevant phenomenological analysis

When a small vacuum expectation value of Higgs triplet (\U0001d710∆) 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 Z2-odd vector-like lepton (X) and an Z2-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 particle, whose mass depends on and is close to the mX parameter. Combing the constraints from the DM measurements, the h → γγ decay, and the oblique T -parameter, it is found that the preferred range of v∆ is approximately in the region of 10−5−10−4 GeV; the mass difference between the doubly and the singly charged Higgs is less than 50 GeV, and the influence on the h → Z γ decay is not significant. Using the constrained parameters, we analyze the decays of each Higgs triplet scalar in detail, including the possible three-body decays when the kinematic condition is allowed. It is found that with the exception of doubly charged Higgs, scalar mixing effects play an important role in the Higgs triplet two-body decays when the scalar masses are near-degenerate. In the non-degenerate mass region, the branching ratios of the Higgs triplet decays are dominated by the three-body decays.

Theory and phenomenology of a two-Higgs-doublet type-II seesaw model at the LHC run 2

We study the most popular scalar extension of the Standard Model, namely the Two Higgs doublet model, extended by a complex triplet scalar (2HDMcT). Such considering model with a very small vacuum expectation value, provides a solution to the massive neutrinos through the so-called type II seesaw mechanism. We show that the 2HDMcT enlarged parameter space allow for a rich and interesting phenomenology compatible with current experimental constraints. In this paper the 2HDMcT is subject to a detailed scrutiny. Indeed, a complete set of tree level unitarity constraints on the coupling parameters of the potential is determined, and the exact tree-level boundedness from below constraints on these couplings are generated for all directions. We then perform an extensive parameter scan in the 2HDMcT parameter space, delimited by the above derived theoretical constraints as well as by experimental limits. We find that an important triplet admixtures are still compatible with the Higgs data and investigate which observables will allow to restrict the triplet nature most effectively in the next runs of the LHC. Finally, we emphasize new production and decay channels and their phenomenological relevance and treatment at the LHC.

Implementing the inverse type-II seesaw mechanism into the 3-3-1 model

After the LHC is turning on and accumulating more data low scale seesaw mechanisms for small neutrino masses with signature manifesting at TeV scale are gaining more and more attention once they provide neutrino masses at sub-eV scale and can be probed at the LHC. In this regard inverse seesaw mechanism arises as an interesting candidate for performing such proposal. This mechanism is a kind of counterpart of canonical mechanism which requires lepton number be violated explicitly at high energy scale while the inverse one requires the contrary, that lepton number be violated explicitly at low energy scale. There are three ways of performing canonical seesaw mechanism. For each one of it there is its inverse counterpart. Here we restrict our investigation to the study of the inverse type II seesaw mechanism. Our main goal is to implement the mechanism into the 3-3-1 model with right-handed neutrinos, but first we revisit the main ideas and consequences of the inverse type I and II seesaw mechanisms when incorporated into the standard model. In regard to the 3-3-1 model, as interesting result, we show that the mechanism may provide small masses to both the standard neutrinos as well as to the right-handed ones. As phenomenological aspect, its best signature are the doubly charged scalars which are sextet by the 3-3-1 symmetry. We investigate their production at the LHC through the process σ(pp→Z⁎,γ⁎,Z′→Δ++Δ−−) and their signal through four leptons final state decay channel.