We explore an intriguing possibility to test the type-II seesaw mechanism of neutrino mass generation at the Large Hadron Collider (LHC). We show that the lepton-number-violating signatures of heavy Majorana neutrinos N_i (for i=1, 2, 3) and doubly-charged Higgs bosons H^++(H^--) can be closely correlated with each other in a class of TeV-scale type-II seesaw models. Taking the minimal version of such models for example, we calculate the cross sections of pp -> l^+_αl^+_βX (l^-_αl^-_βX) processes mediated separately by N_1 and H^++(H^--), and illustrate their nontrivial correlation at the LHC.
Searches for $ΔL=2$ decays are crucial to disentangle the Dirac vs Majorana nature of neutrinos. While neutrinoless nuclear double beta decays are the most promising tool to look for di-electron signals of $ΔL=2$, searches of di-lepton channels with other flavors are far less limited by statistics. We revisit the calculation of $ΔL=2$ decays of hyperons $B^-_i\to B^+_f\ell^-\ell'^-$. We compute the rates of these decays by including the hyperon form factors, which yields finite results in the one-loop model mechanism involving Majorana neutrinos (long-range contributions). In addition, we stud…
We study a model with Majorana neutrino masses generated through doubly charged scalars at two-loop level. We give explicit relationships between the neutrino masses and the same sign dilepton decays of the doubly charged scalars. In particular, we demonstrate that at the tribimaximal limit of the neutrino mixings, the absolute neutrino masses and Majorana phases can be extracted through the measurements of the dilepton modes at colliders.
The recent observation of the smallest neutrino mixing angle $θ_{13}$ in the Daya Bay and RENO experiments motivates us to examine whether $θ_{13} \simeq 9^\circ$ at the electroweak scale can be generated from $θ_{13} = 0^\circ$ at a superhigh-energy scale via the radiative corrections. We find that it is difficult but not impossible in the minimal supersymmetric standard model (MSSM), and a relatively large $θ_{13}$ may have some nontrivial impacts on the running behaviors of the other two mixing angles and CP-violating phases. In particular, we demonstrate that the CP-violating phases play a…
We discuss a 331 model with three scalar triplets and neutral fermion singlets. We show that in the 331 model with right-handed neutrinos, it is possible to obtain small active neutrino masses via the double and inverse seesaw mechanisms, without the use of scalar sextets or triplets with doubly-charged Higgs. Two types of models are discussed. If we have a large Majorana mass matrix for the singlets, the spectrum of neutrinos presents light, heavy and very heavy masses. The other possibility is a small (zero) Majorana mass matrix, which leads to pseudo-Dirac (Dirac) heavy neutrinos in the TeV…
In the minimal extension of the standard electroweak theory with ultra massive Majorana neutrinos, the process e- + e- -> mu- + mu- could be observable, in sharp contrast with the reaction e- + e- -> W- + W- which is entirely controlled by neutrinoless double beta decay $ββ_{0 ν}$ data. Our result provides the process background that must be confronted "new physics" models which postulate doubly charged particles, such as the gauge bilepton Y^{-} in the $SU(3)_{\rm c} \times SU(3)_{\rm L} \times U(1)$ model, the left-right $SU(2)_{\rm L} \times SU(2)_{\rm R} \times U(1)_{\rm B-L}$ one, and its…
Neutrino masses may be generated by the VEV of an $SU(2)_L$ Higgs triplet. We assume that the doubly charged component of such a triplet has a mass in the range of several 100 GeV, such that it is accessible at LHC. Its decay into like-sign leptons provides a clean experimental signature, which allows for a direct test of the neutrino mass matrix. By exploring the branching ratios of this decay into leptons of various flavours, we show that within this model the type of the neutrino mass spectrum (normal, inverted or quasi-degenerate) might actually be resolved at the LHC. Furthermore, we show…
The rate for the lepton-number-violating decay K+ to pi- mu+mu+ is calculated in a model which incorporates doubly-charged Higgs bosons. We find that for reasonable values of the parameters the decay branching ratio may be as large as 2E-16. Although this is a discouragingly small number, it is of the same order of magnitude as the rate mediated by massive Majorana neutrinos.
The lepton-number-violating decays of $B^+, D^+$ and $D_s^+$ mesons induced by the doubly charged Higgs boson have been studied. It is found that although the yielded results of the branch ratio are much smaller than the present limits from the data they are consistent with the previous conclusions calculated in the framwork of relativistic quark model where the processes happened via the light Majorana neutrinos.
The latest results from atmospheric and accelerator neutrino experiments indicate that the normal neutrino mass ordering $m^{}_1 < m^{}_2 < m^{}_3$, a maximal leptonic CP-violating phase $δ= 270^\circ$ and the second octant of neutrino mixing angle $θ^{}_{23} > 45^\circ$ are favored. In light of new experimental results, we update previous phenomenological studies on two-zero textures of the Majorana neutrino mass matrix $M^{}_ν$, in the flavor basis where the charged-lepton mass matrix $M^{}_l$ is diagonal. When the $1σ$ ranges of neutrino mixing parameters are taken into account, only four (…
The process $e^- γ\to e^+ W_R^- W_R^-$ is studied in the framework of the Left-Right symmetric model. It is shown that this reaction and $e^- γ\to l^+ W_R^- W_R^-$ for the arbitrary final lepton are likely to be discovered for CLIC collider option. For relatively light doubly charged Higgs boson its mass does not have much influence on the discovery potential, while for heavier values the probability of the reaction increases.
We have investigated in detail a model that contains an additional SU(2) singlet and triplet scalar fields than the Standard Model (SM). This allows the radiative generation of Majorana neutrino masses at two-loop order with the help of doubly charged Higgs bosons that arise from the extended Higgs sector. We studied in detail the phenomenology of the Higgs and neutrino sectors of the model. We give the analytical form of the masses of scalar and pseudoscalar bosons and their mixings, and the structure of the active neutrino mass matrix. It is found that the model accommodates only normal neut…
We extend some two Higgs doublet models, where the Yukawa couplings for the charged fermion mass generation only involve one Higgs doublet, by two singlet scalars respectively carrying a singly electric charge and a doubly electric charge. The doublet and singlet scalars together can mediate a two-loop diagram to generate a tiny Majorana mass matrix of the standard model neutrinos. Remarkably, the structure of the neutrino mass matrix is fully determined by the symmetric Yukawa couplings of the doubly charged scalar to the right-handed leptons. Meanwhile, a one-loop induced neutrinoless double…
We examine the same-sign single dilepton productions of $\ell_i^{\pm}\ell_j^{\pm} (\ell_{i,j}=e,μ)$ in high-energy proton-proton collisions at the Large Hadron Collider (LHC) in models with doubly charged Higgs scalars as well as heavy Majorana neutrinos. We demonstrate that these spectacular productions can be detected at the LHC for a class model in which the doubly charged Higgs scalars couple only to the right-handed charged leptons. The ranges of the possible doubly charged Higgs masses and mixings to observe the processes at the LHC are discussed.
Doubly charged Higgs bosons (H^++) are a distinctive signature of the Higgs Triplet Model of neutrino mass generation. If H^++ is relatively light (m_{H^++} < 400GeV) it will be produced copiously at the LHC, which could enable precise measurements of the branching ratios of the decay channels H^++ to l_i l_j. Such branching ratios are determined solely by the neutrino mass matrix which allows the model to be tested at the LHC. We quantify the dependence of the leptonic branching ratios on the absolute neutrino mass and Majorana phases, and present the permitted values for the channels ee, emu…
We further study a predictive model for the masses and mixing matrix of three Majorana neutrinos. At zeroth order the model yielded degenerate neutrinos and a generalized ``tribimaximal" mixing matrix. At first order the mass splitting was incorporated and the tribimaximal mixing matrix emerged with very small corrections but with a zero value for the parameter $s_{13}$. In the present paper a different, assumed weaker, perturbation is included which gives a non zero value for $s_{13}$ and further corrections to other quantities. These corrections are worked out and their consequences discusse…
We present a systematic comparison of doubly charged Higgs boson production mechanisms at hadron colliders in the context of the Type II Seesaw model, emphasizing the importance of higher-order corrections and subdominant channels. We consider the Drell-Yan channel at next-to-leading order in QCD, photon fusion at leading order, gluon fusion with resummation of threshold logarithms up to next-to-next-to-next-to-leading logarithmic accuracy, and same-sign weak boson fusion at next-to-leading order in QCD. For Drell-Yan processes, we study the impact of a static jet veto at next-to-leading order…
We study the pair production of doubly charged Higgs bosons at the Large Hadron Collider (LHC), assuming the doubly charged Higgs to be part of an SU(2)_L triplet which generates Majorana masses for left-handed neutrinos. Such pair-production has the advantage that it is not constrained by the triplet vacuum expectation value, which tends to make the single production rate rather small. We point out that, in addition to the Drell-Yan (DY) production mechanism, two-photon processes also contribute to H++H++ production at a level comparable to the QCD corrections to the DY channel. Decays of the…
If the massive neutrinos are identified to be the Majorana particles via a convincing measurement of the neutrinoless double beta (0νββ) decay, how to determine the Majorana CP-violating phases in the 3 x 3 lepton flavor mixing matrix U will become a desirable experimental question. The answer to this question is to explore all the possible lepton-number-violating (LNV) processes in which the Majorana phases really matter. In this paper we carry out a systematic study of CP violation in neutrino-antineutrino oscillations, whose CP-conserving parts involve six independent 0νββ-like mass terms <…
The electric dipole moments (EDMs) of charged leptons are significantly suppressed in standard model. It has been found previously that they are even more severely suppressed in seesaw type models by powers of tiny neutrino masses as far as a leptonic CP source is concerned. We investigate whether a Majorana-type Yukawa coupling between charged leptons and a doubly charged scalar can contribute significantly to their EDMs. An observable EDM would then help unravel the Majorana nature of neutrinos by a lepton number conserving quantity. We find that the EDMs are indeed parametrically large, of …
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…
Assuming the Higgs triplet model, we obtain the bounds on the absolute neutrino mass and the unknown MNS parameters by measuring decay processes of doubly charged particles at the CERN LHC. Majorana CP violating phases affect the prediction rather seriously, which is served to restrict these phases.
A natural extension of the standard $SU(2)_{\rm L} \times U(1)_{\rm Y}$ gauge model to accommodate massive neutrinos is to introduce one Higgs triplet and three right-handed Majorana neutrinos, leading to a $6\times 6$ neutrino mass matrix which contains three $3\times 3$ sub-matrices $M_{\rm L}$, $M_{\rm D}$ and $M_{\rm R}$. We show that three light Majorana neutrinos (i.e., the mass eigenstates of $ν_e$, $ν_μ$ and $ν_τ$) are exactly massless in this model, if and only if $M_{\rm L} = M_{\rm D} M_{\rm R}^{-1} M_{\rm D}^T$ exactly holds. This no-go theorem implies that small but non-vanishing …
In the conventional type-(I+II) seesaw model, the effective mass matrix of three known light neutrinos is given by M_nu = M_L - M_D M^{-1}_R M^T_D in the leading-order approximation. We propose an intriguing scenario, in which the structural cancellation condition M_D M^{-1}_R M^T_D = 0 is guaranteed by the A_4 x Z_2 flavor symmetry. As a consequence, neutrino masses are mainly generated by the Higgs triplet M_nu = M_L, while the neutrino mixing matrix is non-unitary and takes on the nearly tri-bimaximal pattern. A discriminating feature of this scenario from the pure type-II seesaw model is t…
We study the phenomenology of the type-II seesaw model at a linear e^-e^- collider. We show that the process e^-e^- \rightarrow alpha^-beta^- (alpha, beta = e, mu, tau being charged leptons) mediated by a doubly charged scalar is very sensitive to the neutrino parameters, in particular the absolute neutrino mass scale and the Majorana CP-violating phases. We identify the regions in parameter space in which appreciable collider signatures in the channel with two like-sign muons in the final state are possible. This includes Higgs triplet masses beyond the reach of the LHC.
We examine how a scenario of coexisting two-particle dark mater can be realized in the extended seesaw model, which we have proposed previously to accommodate small neutrino masses and low scale leptogenesis with an introduction of singlet Majorana neutrino $S$ and singlet scalar $ϕ$. We now impose the discrete symmetry $Z_2 \times Z_2^{\prime}$ and introduce new renormalizable interaction terms with a new heavy singlet scalar particle $Φ$ so as for previously introduced $S$ and $ϕ$ to be doubly coexisting dark matter candidates. Depending on the mass spectrum of the two dark matter candidates…
The dileptonic decays of doubly-charged Higgs bosons H^{\pm\pm} are investigated in the minimal type-II seesaw model with one Higgs triplet Δand one heavy Majorana neutrino N_1 at the TeV scale. We show that the branching ratios {\cal B}(H^{\pm\pm} \to l^\pm_αl^\pm_β) depend not only on the mass and mixing parameters of three light neutrinos ν_i (for i=1,2,3), but also on those of N_1. Assuming the mass of N_1 to lie in the range 200 GeV--1 TeV, we figure out the generous interference bands for the contributions of ν_i and N_1 to {\cal B}(H^{\pm\pm} \to l^\pm_αl^\pm_β): \sqrt{|\sinθ_{i4} \sinθ…
We propose a model, in the framework of 5D with warped geometry, in which small neutrino Majorana masses are generated by tree level coupling of lepton doublets to a SU(2)_{L}-triplet scalar field, which is coupled to a bulk SM-singlet. The neutrino mass scale is determined by the bulk mass term (alpha_{S}) of the singlet as ve^{-2(alpha_{S}-1)*pi*kR}. This suppression is due to a small overlap between the profile of the singlet zero mode and the triplet, which is confined to the TeV brane. The generic form for the neutrino mass matrix due to the overlap between the fermions is not compatible …
We study the models with the Majorana neutrino masses generated radiatively by two-loop diagrams due to the Yukawa $ρ\bar \ell_R^c \ell_R$ and effective $ρ^{\pm\pm} W^\mp W^\mp$ couplings along with a scalar triplet $Δ$, where $ρ$ is a doubly charged singlet scalar, $\ell_R$ the charged lepton and $W$ the charged gauge boson. A generic feature in these types of models is that the neutrino mass spectrum has to be a normal hierarchy. Furthermore, by using the neutrino oscillation data and comparing with the global fitting result in the literature, we find a unique neutrino mass matrix and predic…
The CDF collaboration has recently published a precision measurement of the W-boson mass that differs from the Standard Model prediction by seven standard deviations. This result can be explained with additional electroweak multiplets that either break the custodial symmetry or contribute to oblique parameters at loop level. Here, we study one of the best-motivated scenarios involving new multiplets: the type-II seesaw model, which involves a scalar triplet that generates Majorana neutrino masses and can furthermore resolve the W-boson mass discrepancy. This favors a doubly-charged scalar with…
If the observed light neutrino masses are induced by their Yukawa couplings to singlet right-handed neutrinos, natural smallness of those renders direct collider tests of the electroweak scale neutrino mass mechanisms almost impossible both in the case of Dirac and Majorana (seesaw of type I) neutrinos. However, in the triplet Higgs seesaw scenario the smallness of light neutrino masses may come from the smallness of B-L breaking parameters, allowing sizable Yukawa couplings even for a TeV scale triplet. We show that, in this scenario, measuring the branching fractions of doubly charged Higgs …
A natural extension of the standard model to accommodate massive neutrinos is to introduce one Higgs triplet and three right-handed Majorana neutrinos, leading to a 6 \times6 neutrino mass matrix. We show that three light Majorana neutrinos (i.e., the mass eigenstates of ν_e, ν_μand ν_τ) are exactly massless, if and only if M_L = M_D M^{-1}_R M^T_D exactly holds in this seesaw model. We propose three simple Type-II seesaw scenarios with broken A_4 \times U(1)_X flavor symmetry to interpret the observed neutrino mass spectrum and neutrino mixing pattern. Such a TeV-scale neutrino model can be t…
We have investigated the three vector boson production in electron-electron collisions in the framework of the left-right symmetric electroweak model. The process occurs due to lepton number violating interactions mediated by Majorana neutrinos and triplet Higgs scalars. We find that only the reactions with a heavy gauge boson pair in the final state, $e^-e^-\to W^{-}_2 W^{-}_2γ$ and $e^-e^- \to W^{-}_2 W^{-}_2Z^0_1$, are phenomenologically interesting from the point of view of the Next Linear Collider. If the mass of $W_2^-$ is 0.5 TeV and the mass of the heavy Majorana neutrino of the order …
Adding a fermion to the standard model particle content which is a fiveplet under $SU(2)_L$ gives a dark matter candidate. The lightest state in the multiplet is neutral and automatically stable. The charged component of the multiplet is only slightly heavier and can travel a finite distance in the LHC detectors before decaying, leaving a charged track which disappears before the edge of the detector. We use the recent ATLAS and CMS searches to exclude a Majorana fiveplet with a mass up to 267 GeV. We estimate that with 3 ab$^{-1}$ of $\sqrt{s}=14$ TeV data this could be pushed to a mass 520 G…
We demonstrate how to systematically test a well-motivated mechanism for neutrino mass generation (Type-II seesaw) at the LHC, in which a Higgs triplet is introduced. In the optimistic scenarios with a small Higgs triplet vacuum expectation value vd < 10^{-4} GeV, one can look for clean signals of lepton number violation in the decays of doubly charged and singly charged Higgs bosons to distinguish the Normal Hierarchy (NH), the Inverted Hierarchy (IH) and the Quasi-Degenerate (QD) spectrum for the light neutrino masses. The observation of either H+ --> tau+ nubar or H+ --> e+ nubar will be pa…
We propose a radiative seesaw model with an inert triplet scalar field in which Majorana neutrino masses are generated at the two loop level. There are fermionic or bosonic dark matter candidates in the model. We find that each candidate can satisfy the WMAP data when its mass is taken to be around the half of the mass of the standard model like Higgs boson. We also discuss phenomenology of the inert triplet scalar bosons, especially focusing on the doubly-charged scalar bosons at Large Hadron Collider in parameter regions constrained by the electroweak precision data and WMAP data. We study h…
In the {\sl type II seesaw} model, if spontaneous violation of the lepton number conservation prevails over that of explicit violation, a rich Higgs sector phenomenology is expected to arise with light scalar states having mixed charged-fermiophobic/neutrinophilic properties. We study the constraints on these light CP-even ($h^0$) and CP-odd ($A^0$) states from LEP exclusion limits, combined with the so far established limits and properties of the $125-126$~GeV ${\cal H}$ boson discovered at the LHC. We show that, apart from a fine-tuned region of the parameter space, masses in the $\sim 44$ t…
The connection between the neutrinoless double beta ((ββ)_{0 ν}-) decay effective Majorana mass, |M_{ee}|, and the branching ratios of the decays H^{\pm\pm}\to l^\pm {l'}^\pm, l,{l'}= e,μ, of the doubly charged Higgs boson H^{\pm\pm} is analysed within the Higgs Triplet Model of neutrino mass generation. We work in the version of the model with explicit breaking of the total lepton charge conservation, in which H^{\pm\pm}\to l^\pm {l'}^\pm, l,{l'} = e,μ,τ, are the dominant decay modes of H^{\pm\pm}. It is assumed also that H^{\pm\pm} are relatively light so that they can be produced at LHC and…
We propose a three loop radiative neutrino mass scenario with an isolated doubly charged singlet scalar $k^{\pm\pm}$ without couplings to the charged leptons, while two other singly charged scalars $h_1^\pm$ and $h_2^\pm$ attach to them. In this setup, the lepton flavor violation originating from $k^{\pm\pm}$ exchanges is suppressed and the model is less constrained, where some couplings can take sizable values. As reported in our previous work, the loop suppression factor at the three loop level would be too strong and realized neutrino masses in a three loop scenario could be smaller than th…
We propose a new mechanism where both Dirac masses for the charged-leptons and Majorana masses for neutrinos are generated via quantum levels. The charged-lepton masses are given by the vacuum expectation values (VEVs) of the Higgs doublet field and that of a triplet field. On the other hand, neutrino masses are generated by two VEVs of triplet Higgs fields. As a result, the hierarchy between the masses for charged-leptons and neutrinos can be explained by the triplet VEVs which have to be much smaller than the doublet VEV due to the constraint from the electroweak rho parameter. We construct …
We study the origin of neutrino mass through lepton-number violation and spontaneous $U(1)_{L_μ-L_τ}$ symmetry breaking. To accomplish the purpose, we include one Higgs triplet, two singlet scalars, and two vector-like doublet leptons in the $U(1)_{L_μ-L_τ}$ gauge extension of the standard model. To completely determine the free parameters, we employ the Frampton-Glashow-Marfatia (FGM) two-zero texture neutrino mass matrix as a theoretical input. It is found that when some particular Yukawa couplings vanish, an FGM pattern can be achieved in the model. Besides the explanation of neutrino data,…
In Type III seesaw model the heavy neutrinos are contained in leptonic triplet representations. The Yukawa couplings of the triplet fermion and the left-handed neutrinos with the doublet Higgs field produce the Dirac mass terms. Together with the Majorana masses for the leptonic triplets, the light neutrinos obtain non-zero seesaw masses. We point out that it is also possible to have a quadruplet Higgs field to produce the Dirac mass terms to facilitate the seesaw mechanism. The vacuum expectation value of the quadruplet Higgs is constrained to be small by electroweak precision data. Therefore…
We present a comprehensive analysis of the Higgs boson spectra in several versions of the supersymmetric left--right model based on the gauge symmetry $SU(3)_c \times SU(2)_L \times SU(2)_R \times U(1)_{B-L}$. A variety of symmetry breaking sectors are studied, with a focus on the constraints placed on model parameters by the lightest neutral CP even Higgs boson mass $M_h$. The breaking of $SU(2)_R$ symmetry is achieved by Higgs fields transforming either as triplets or doublets, and the electroweak symmetry breaking is triggered by either bi--doublets or doublets. The Higgs potential is analy…
