We present two models where the familiar leptonic symmetry $L_e-L_μ-L_τ$ is a gauge symmetry. We show how anomaly cancellation constrains the allowed theories, with one of them requiring a fourth sequential chiral standard model fermion generation and a second one with three generations, requiring gauging of $(L_e-L_μ-L_τ)-(B_1-B_2-B_3)$ with $B_a$ representing the baryon number of the $a$th generation quarks. Unlike global $L_e-L_μ-L_τ$ models which always leads to inverted mass hierarchy for neutrinos, the gauged version can lead to normal hierarchy. We show how to construct realistic models in both the cases and discuss the dark matter candidate in both. In our model, the breaking of $U(1)_{L_e-L_μ-L_τ}$ is responsible for neutrino mass via type-I mechanism whereas the real part of $U(1)_{L_e-L_μ-L_τ}$ breaking scalar field (called $ϕ$ here) plays the role of freeze-in dark matter candidate. Since $ϕ$ is unstable, for it to qualify as dark matter, its lifetime must be larger than the age of the Universe, implying that the relic of $ϕ$ is generated through freeze-in mechanism and its mass must be less than an MeV. We also discuss the possibility of explaining both muon and electron $(g-2)$ while being consistent with the dark matter relic density and lifetime constraints.
We reexamine sterile neutrino dark matter in gauged $U(1)_{B-L}$ model. Improvements have been made by tracing and careful evaluation of the evolution of the number densities of sterile neutrinos $N$ and extra neutral gauge bosons $Z'$. As a result, the cosmologically-interesting gauge coupling of $U(1)_{B-L}$ for freeze-in sterile neutrinos turns out to be smaller than the values reported in the literature. This avoids the overproduction of $Z'$ so that it is consistent with the big bang nucleosynthesis and the cosmic microwave background constraints on the effective number of neutrino specie…
We propose a simple extension of the standard model where neutrinos get naturally small "scotogenic" Dirac masses from an unbroken gauged $B-L$ symmetry, ensuring dark matter stability. The associated gauge boson gets mass through the Stueckelberg mechanism. Two scenarios are identified, and the resulting phenomenology briefly sketched.
We propose a new gauged $B-L$ extension of the standard model where light neutrinos are of Dirac type, naturally acquiring sub-eV mass after electroweak symmetry breaking, without any additional global symmetries. This is realised by choosing a different $B-L$ charge for right handed neutrinos than the usual $-1$ so that the Dirac Yukawa coupling involves an additional neutrinophilic scalar doublet instead of the usual Higgs doublet. The model can be made anomaly free by considering four additional chiral fermions which give rise to two massive Dirac fermions by appropriate choice of singlet s…
We study the possibility of right-handed neutrino dark matter (DM) in gauged $U(1)_{B-L} \times Z_2$ extension of the standard model augmented by an additional scalar doublet, being odd under the $Z_2$ symmetry, to give rise the scotogenic scenario of radiative neutrino masses. Due to lepton portal interactions, the right-handed neutrino DM can have additional co-annihilation channels apart from the usual annihilations through $Z_{B-L}$ which give rise to much more allowed mass of DM from relic abundance criteria, even away from the resonance region like $M_{\rm DM} \approx M_{Z_{B-L}}/2$. Thi…
We discuss a new radiative seesaw model with the gauged B$-$L symmetry which is spontaneously broken. We improve the previous model by using the anomaly-free condition without introducing too many fermions. In our model, dark matter, tiny neutrino masses and neutrino oscillation data can be explained simultaneously, assuming the B$-$L symmetry breaking at the TeV scale.
We study a neutrino model introducing an additional nontrivial gauged lepton symmetry where the neutrino masses are induced at two-loop level while the first and second charged-leptons of the standard model are done at one-loop level. As a result of model structure, we can predict one massless active neutrino, and there is a dark matter candidate. Then we discuss neutrino mass matrix, muon anomalous magnetic moment, lepton flavor violations, oblique parameters, and relic density of dark matter taking into account the experimental constraints.
If a Z' gauge boson of a gauged L_mu - L_tau symmetry is very light, it is associated with a long-range leptonic force. In this case the particles in the Sun create via mixing of Z' with the Standard Model Z a flavor-dependent potential for muon neutrinos in terrestrial long-baseline experiments. The potential changes sign for anti-neutrinos and hence can lead to apparent differences in neutrino and anti-neutrino oscillations without introducing CP or CPT violation. This could for instance explain the recently found discrepancy in the survival probabilities of muon neutrinos and anti-neutrinos…
We propose a predictively radiative neutrino mass model with gauged $U(1)_{B-2L_{\ell_2}-L_{\ell_1}}$ symmetry in which we successfully realize two-zero textures of neutrino mass matrix depending on charge assignment for leptons and the singlet scalar fields. Then some correlations of neutrino parameters are shown where we take mass structure given by $(\ell_2, \ell_1) = (μ, τ)$ or $(μ, e)$ as a representative case. Furthermore we discuss phenomenology of the model such as lepton flavor violations, collider physics, and dark matter candidate.
Massive neutrino is an evidence of new physics beyond the Standard Model. One of the well motivated new physics scenarios is a model with gauged lepton flavor symmetry. We investigate neutrino properties in the minimal SU$(3)_\ell\times$SU$(3)_E$ gauged lepton flavor model. In this model, three new species of fermions are introduced to cancel gauge anomalies. These new fermions lead to a see-saw mechanism for neutrino mass generation. We impose the constraints from perturbative unitarity in 2-2 scattering processes, as well as current experimental constraints, to obtain viable neutrino spectru…
We discuss a classically conformal radiative neutrino model with gauged B$-$L symmetry, in which the B$-$L symmetry breaking can occur through the Coleman-Weinberg mechanism. As a result, Majorana mass term is generated and EW symmetry breaking also occurs. We show some allowed parameters to satisfy several theoretical and experimental constraints. Theoretical constraints are inert conditions and Coleman-Weinberg condition. Experimental bounds are lepton flavor violation(especially μ-> e γ), the current bound on the $Z'$ mass at LHC, in additions to the neutrino oscillations.
We study neutrino and dark matter based on a gauged $U(1)_R$ symmetry in a framework of radiative seesaw scenario. Identifying dark matter as a bosoninc particle, it interacts with quark and lepton sectors through vector-like heavier quark and leptons, and plays an role in generating neutrino mass matrix together with neutral heavier fermions. We explore several constraints for masses and couplings related to dark matter by computing relic density and direct search, taking the neutrino oscillation, lepton flavor violations, and muon anomalous magnetic moment into account. Finally, we briefly m…
Despite the popularity of two-Higgs-doublet models (2HDMs) with a gauged abelian flavor symmetry, the allowed Yukawa textures have only been partly explored so far. In this work, we classify and compare every anomaly-free instance, in the case of having two generations of right-handed neutrinos and a type-I seesaw mechanism. We found 16 valid implementations in total, out of which 11 agree well with current experimental bounds. To our knowledge, neither of these models have been considered previously.
We present a simple extension of the Standard Model that leads to renormalizable long-range vector-mediated neutrino self-interactions. This model can resolve the Hubble tension by delaying the onset of neutrino free-streaming during recombination, without conflicting with other measurements. The extended gauge, scalar and neutrino sectors lead to observable signatures, including invisible Higgs and $Z$ decays, thereby relating the Hubble tension to precision measurements at the LHC and future colliders. The model has a new neutrinophilic gauge boson with $m_{Z'}\sim\mathcal{O}(10~\mathrm{eV})…
We explore muon anomalous magnetic moment (muon $g-2$) in a scotogenic neutrino model with a gauged lepton number symmetry $U(1)_{μ-τ}$. In this model, a dominant muon $g-2$ contribution comes not from an additional gauge sector but from a Yukawa sector. In our numerical $Δχ^2$ analysis, we show that our model is in favor of normal hierarchy with some features. We demonstrate one benchmark point, satisfying muon $g-2$ at the best fit value $25.1\times10^{-10}$.
If a Z' gauge boson from a gauged L_mu - L_tau symmetry is very light, it is associated with a long-range leptonic force. In this case the particles in the Sun create via mixing of the Z' with the Standard Model Z a flavor-dependent potential for muon neutrinos in terrestrial long-baseline experiments. The potential changes sign for anti-neutrinos and hence can lead to apparent differences in neutrino and anti-neutrino oscillations without introducing CP or CPT violation. This could for instance explain the recently found discrepancy in the MINOS experiment. We obtain the associated parameters…
We present the radiative corrections to neutrino masses in a minimal supersymmetric extension of the standard model with local $U(1)_{B-L}$ symmetry. At tree level, three tiny active neutrinos and two nearly massless sterile neutrinos can be obtained through the seesaw mechanism. Considering the one-loop corrections to the neutrino masses, the numerical results indicate that two sterile neutrinos obtain ${\rm KeV}$ masses and the small active-sterile neutrino mixing angles. The lighter sterile neutrino is a very interesting dark matter candidate in cosmology. Meanwhile the active neutrinos mix…
Lepton number is promoted to an $U(1)_L$ gauge symmetry in a simple extension of the standard model. The spontaneous breaking of $U(1)_L$ by three units allows a conserved $Z_3^L$ lepton symmetry to remain, guaranteeing that neutrinos are Dirac fermions, which acquire naturally small masses from a previously proposed mechanism. Dark matter appears as a singlet scalar, with dark symmetry $Z_3^D$ derivable from $Z_3^L$. Muon $g-2$ may be explained.
If the minimal standard model of quarks and leptons is extended to include just a righthanded partner to nu_tau, then the quantum number B-3L_tau can be added as a gauge symmetry without the appearance of anomalies. A suitable extension of the scalar sector allows one neutrino to have a seesaw mass, and the other two to have radiative masses, with acceptable phenomenological values for neutrino oscillations. The B-3L_tau gauge boson may be light and be observable through its decay into tau^+ tau^-.
Extending the Minimal Supersymmetric Standard Model (MSSM) to explain small neutrino masses via the inverse seesaw mechanism can lead to a new light supersymmetric scalar partner which can play the role of inelastic dark matter (iDM). It is a linear combination of the superpartners of the neutral fermions in the theory (the light left-handed neutrino and two heavy Standard Model singlet neutrinos) which can be very light with mass in $\sim 5-20$ GeV range, as suggested by some current direct detection experiments. The iDM in this class of models has keV-scale mass splitting, which is intimatel…
Building up on previous work we propose a Dark Matter (DM) model with gauged matter parity and dynamical gauge coupling unification, driven by the same physics responsible for scotogenic neutrino mass generation. Our construction is based on the extended gauge group \3311, whose spontaneous breaking leaves a residual conserved matter parity, $M_{P}$, stabilizing the DM particle candidates of the model. A key role is played by the Majorana ${\rm SU(3)_{L}}$-octet leptons, in allowing successful gauge coupling unification and one-loop scotogenic neutrino mass generation. Theoretical consistency …
We consider the gauging of $L_μ- L_τ$ as an explanation of a possibly large muon anomalous magnetic moment. We then show how neutrino masses with bimaximal mixing may be obtained in this framework. We study the novel phenomenology of the associated gauge boson in the context of present and future high-energy collider experiments.
Gauged $U(1)_{L_μ- L_τ}$ model has been advocated for a long time in light of muon $g-2$ anomaly, which is a more than $3σ$ discrepancy between the experimental measurement and the standard model prediction. We augment this model with three right-handed neutrinos $(N_e, N_μ, N_τ)$ and a vector-like singlet fermion $(χ)$ to explain simultaneously the non-zero neutrino mass and dark matter content of the Universe, while satisfying anomalous muon $g-2$ constraints. It is shown that in a large parameter space of this model we can explain positron excess, observed at PAMELA, Fermi-LAT and AMS-02, t…
We propose a radiative seesaw model with a hidden $U(1)$ gauge symmetry. In order to have anomaly cancellations, we need to introduce several new fermions that contribute to muon anomalous magnetic dipole moment $(g-2)_μ$ as well as explain the neutrino oscillation data. We also consider a fermionic dark matter candidate that correlates with $(g-2)_μ$ and neutrino mass matrix at the same time. We show allowed regions in our input parameters satisfying several constraints. Finally, we also briefly discuss the possibility of the resolution of the Hubble tension via neutrino self-interactions med…
The gauged $B - L$ symmetry is one of the simplest and well studied extension of standard model. In the conventional case, addition of three singlet right handed neutrinos each transforming as $-1$ under the $B - L$ symmetry renders it anomaly free. It is usually assumed that the $B - L$ symmetry is spontaneously broken by a singlet scalar having two units of $B - L$ charge, resulting in a natural implementation of Majorana seesaw mechanism for neutrinos. However, as we discuss in this proceeding, there is another simple anomaly free solution which leads to Dirac or inverse seesaw masses for n…
We consider gauged U(1) extensions of the standard model of particle physics with three right-handed sterile neutrinos and a singlet scalar. The neutrinos obtain mass via the type I seesaw mechanism. We compute the one loop corrections to the elements of the tree level mass matrix of the light neutrinos and show explicitly the cancellation of the gauge dependent terms. We present a general formula for the gauge independent, finite one-loop corrections for arbitrary number new U(1) groups, new complex scalars and sterile neutrinos. We estimate the size of the corrections relative to the tree le…
In both scotogenic neutrino and flavor dark matter models, the dark sector communicates with the standard model fermions via Yukawa portal couplings. We propose an economic scenario that scotogenic neutrino and flavored mediator share the same inert Higgs doublet and all are charged under a hidden gauged $U(1)$ symmetry. The dark Z2 symmetry in dark sector is regarded as the remnant of this hidden $U(1)$ symmetry breaking. In particular, we investigate a dark $U(1)_D$ (and also a $U(1)_{B-L}$) model which unifies scotogenic neutrino and top-flavored mediator. In this model dark tops and dark n…
We analyze a model with unbroken B-L gauge symmetry where neutrino masses are generated at one loop, after spontaneous breaking of a global U(1) symmetry. These symmetries ensure dark matter stability and the Diracness of neutrinos. Within this context, we examine fermionic dark matter. Consistency between the required neutrino mass and the observed relic abundance indicates dark matter masses and couplings within the reach of direct detection experiments.
It is well known that the differences between the lepton numbers can be gauged with the Standard Model matter content. Such extended gauge theories, dubbed as the gauged U(1)$_{L_α- L_β}$ models, have been widely discussed so far as potential candidates for physics beyond the Standard Model. In this work, we study the minimal versions of these gauge theories, where three right-handed neutrinos as well as a single U(1)$_{L_α- L_β}$ symmetry breaking Higgs field---an SU(2)$_L$ singlet or doublet---are introduced. In these minimal models, the neutrino mass terms are constrained by the gauge symme…
Universidad Técnica Federico Santa María（费德里科·圣玛丽亚技术大学）；Centro Científico-Tecnológico de Valparaíso（瓦尔帕莱索科技中心）；Millennium Institute for Subatomic Physics at High-Energy Frontier (SAPHIR)（高能前沿子物理千年研究所（SAPHIR））；Universidad de Guanajuato（瓜纳华托大学）；Universidad Andres Bello（安德烈斯·贝略大学）；Universidad Nacional Autónoma de México（墨西哥国立自治大学）；Secretaría de Ciencia, de Humanidades, Tecnología e Innovación（科学、人文、技术与创新秘书处）
An extension of the Standard Model with anomaly free $U(1)_F$ flavor symmetry is studied in this paper. With this extension and the addition of the right-handed neutrino states, the solution of anomaly free charge assignments is found, which gives appealing texture zero and hierarchical Yukawa matrices. This gives us a natural understanding of the hierarchies between charged fermion masses and Cabibbo-Kobayashi-Maskawa (CKM) matrix elements. Neutrino Dirac and Majorana coupling matrices also have desirable structures leading to successful neutrino oscillations with inverted neutrino mass order…
We propose a one-loop induced neutrino mass model with hidden $U(1)$ gauge symmetry, in which we successfully involve a bosonic dark matter (DM) candidate propagating inside a loop diagram in neutrino mass generation to explain the $e^+e^-$ excess recently reported by the DArk Matter Particle Explorer (DAMPE) experiment. In our scenario dark matter annihilates into four leptons through $Z'$ boson as DM DM $\to Z' Z' (Z' \to \ell^+ \ell^-)$ and $Z'$ decays into leptons via one-loop effect. We then investigate branching ratios of $Z'$ taking into account lepton flavor violations and neutrino osc…
Models of gauged $U(1)_{L_μ-L_τ}$ can provide a solution to the long-standing discrepancy between the theoretical prediction for the muon anomalous magnetic moment and its measured value. The extra contribution is due to a new light vector mediator, which also helps to alleviate an existing tension in the determination of the Hubble parameter. In this article, we explore ways to probe this solution via the scattering of solar neutrinos with electrons and nuclei in a range of experiments and considering high and low solar metallicity scenarios. In particular, we reevaluate Borexino constraints …
The energy spectrum of cosmic neutrinos, which was recently reported by the IceCube collaboration, shows a gap between 400 TeV and 1 PeV. An unknown neutrino interaction mediated by a field with a mass of the MeV scale is one of the possible solutions to this gap. We examine if the leptonic gauge interaction L_μ - L_τ can simultaneously explain the two phenomena in the lepton sector: the gap in the cosmic neutrino spectrum and the unsettled disagreement in muon anomalous magnetic moment. We illustrate that there remains the regions in the model parameter space, which account for both the probl…
We investigate the tree-level neutrino mass generation in the gauged $U(1)_\ell$ lepton model recently proposed by us [arXiv:1805.10382]. With the addition of one Standard Model(SM) singlet, $ϕ_1(Y=0, \ell=1)$, and one SM triplet scalar, $T(Y=-1,\ell=0)$, realistic lepton masses can be accommodated. The resulting magnitude of neutrino mass is given by $\sim v_t^3/v_L^2$, where $v_t$ and $v_L$ are the vacuum expectation values of $T$ and $ϕ_1$, respectively, and it is automatically of the inverse see-saw type. Since $v_L$ is the lepton number violation scale we take it to be high, i.e. ${\cal O…
We propose a new model where the Dirac mass term for neutrinos, the Majorana mass term for right-handed neutrinos, and the other new fermion masses arise via the spontaneous breakdown of the $U(1)_{B-L}$ gauge symmetry. The anomaly-free condition gives four sets of assignment of the B-L charge to new particles, and three of these sets have an associated global $U(1)_{DM}$ symmetry which stabilizes dark matter candidates. The dark matter candidates contribute to generating the Dirac mass term for neutrinos at the one-loop level. Consequently, tiny neutrino masses are generated at the two-loop l…
We propose a one-loop induced radiative neutrino mass model with anomaly free flavour dependent gauge symmetry: $μ$ minus $τ$ symmetry $U(1)_{μ-τ}$. A neutrino mass matrix satisfying current experimental data can be obtained by introducing a weak isospin singlet scalar boson that breaks $U(1)_{μ-τ}$ symmetry, an inert doublet scalar field, and three right-handed neutrinos in addition to the fields in the standard model. We find that a characteristic structure appears in the neutrino mass matrix: two-zero texture form which predicts three non-zero neutrino masses and three non-zero CP-phases fr…
We analyze the distributions of energy, opening angle and invariant mass in muonic neutrino trident production processes, $ν_μ\to ν_μμ\overlineμ$, in a minimal gauged $U(1)_{L_μ- L_τ}$ model, in which the discrepancy of anomalous magnetic moment of muon can be solved. It is known that the total cross sections of the neutrino trident production are degenerate in new physics parameters, the new gauge coupling and gauge boson mass, and therefore other observables are needed to determine these parameters. From numerical analyses, we find that the muon energy and invariant mass distributions show t…
We consider the neutrino sector of a Standard Model with four generations. While the three light neutrinos can obtain their masses from a variety of mechanisms with or without new neutral fermions, fourth-generation neutrinos need at least one new relatively light right-handed neutrino. If lepton number is not conserved this neutrino must have a Majorana mass term whose size depends on the underlying mechanism for lepton number violation. Majorana masses for the fourth generation neutrinos induce relative large two-loop contributions to the light neutrino masses which could be even larger than…
We revisit the current experimental bounds on fourth-generation Majorana neutrino masses, including the effects of right handed neutrinos. Current bounds from LEPII are significantly altered by a global analysis. We show that the current bounds on fourth generation neutrinos decaying to eW and mu W can be reduced to about 80 GeV (from the current bound of 90 GeV), while a neutrino decaying to tau W can be as light as 62.1 GeV. The weakened bound opens up a neutrino decay channel for intermediate mass Higgs, and interesting multi-particle final states for Higgs and fourth generation lepton deca…
We consider a mechanism for neutrino mass generation, based on a local B-L extension of the standard model, which becomes a linear seesaw regime for light neutrinos after spontaneous symmetry breaking. The spectrum of extra particles includes heavy neutrinos with masses near the TeV scale and a heavy Z' boson, as well as three extra neutral scalars and a charged scalar pair. We study the production and decays of these heavy particles at the LHC. Z' will decay mainly into heavy neutrino pairs or charged lepton pairs, similar to other low scale seesaw scenarios with local B-L, while the phenomen…
We present new constraints on the mass $m_{ν_τ}$ of the tau neutrino and its mixing with a fourth generation neutrino. From an analysis of the partial widths of tau lepton decays we obtain the following bounds at the 90% confidence level: $m_{ν_τ} < 32$ MeV and $\sin^2θ< 0.007$, where $θ$ describes the Cabibbo-like mixing of the third and fourth generation neutrinos.
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 …
We propose a scenario of the right-handed neutrino dark matter in the context of the minimal gauged $U(1)_{B-L}$ model by introducing an additional parity which ensures the stability of dark matter particle. The annihilation of this right-handed neutrino takes place dominantly through the s-channel Higgs boson exchange, so that this model can be called Higgs portal dark matter model. We show that the thermal relic abundance of the right-handed neutrino dark matter with help of Higgs resonance can match the observed dark matter abundance. In addition we estimate the cross section with nucleon a…
We investigate the possibility of a fourth sequential generation in the lepton sector. Assuming neutrinos to be Majorana particles and starting from a recent - albeit weak - evidence for a non-zero admixture of a fourth generation neutrino from fits to weak lepton and meson decays we discuss constraints from neutrinoless double beta decay, radiative lepton decay and like-sign dilepton production at hadron colliders. Also an idea for fourth generation neutrino mass model building is briefly outlined. Here we soften the large hierarchy of the neutrino masses within an extradimensional model that…
In an endeavor to explain the light neutrino masses and dark matter (DM) simultaneously, we study a gauged $U(1)_{\rm B-L}$ extension of the standard model (SM). The neutrino masses are generated through a variant of type-II seesaw mechanism in which one of the scalar triplets has a mass in a scale that is accessible at the present generation colliders. Three SM singlet right chiral fermions $χ_{iR}$($i=e,μ,τ$) with $\rm B-L$ charges -4, -4, +5 are invoked to cancel the $\rm B-L$ gauge anomalies and the lightest one among these three fermions becomes a viable DM candidate as their stability is…
Possible single productions of the fourth standard model generation neutrino via anomalous interactions at the future ep colliders are studied. Signatures of such anomalous processes and backgrounds are discussed in detail. Discovery limits for neutrino mass and achievable values of anomalous coupling strength are determined.
We investigate the possibility of a fourth sequential generation in the lepton sector. Assuming neutrinos to be Majorana particles and starting from a recent - albeit weak - evidence for a non-zero admixture of a fourth generation neutrino from fits to weak lepton and meson decays we discuss constraints from neutrinoless double beta decay, radiative lepton decay and like-sign di-lepton production at hadron colliders.
We propose a gauged $U(1)_{B-L}$ extension of the standard model (SM) to explain simultaneously the light neutrino masses and dark matter (DM). The generation of neutrino masses occurs through a variant of type-II seesaw mechanism in which one of the scalar triplets lies at the TeV scale yet have a large dilepton coupling, which paves a path for probing this model at colliders. The gauging of $U(1)_{B-L}$ symmetry in a type-II seesaw framework introduces $B-L$ anomalies. Therefore we invoke three right handed neutrinos $ν_{R_{i}}$(i=1,2,3) with $B-L$ charges -4,-4,+5 to cancel the anomalies. W…
I analyze a fourth generation lepton sector in which the lightest particle is a stable Majorana neutrino. In this scenario fourth generation neutrinos have both a Dirac and Majorana mass, resulting in two Majorana neutrino mass eigenstates. A reanalysis of LEP's lower mass bound is performed on stable Majorana neutrinos from the Z width and the lower mass bound is loosened. I also extrapolate LEP's SUSY squark search with a 2 jet plus missing missing energy final state to the production and decay of a pair of heavy Majorana neutrinos; here it is expected that significant regions of the neutrin…
We evaluate the LHC discovery potential for the fourth family Standard Model neutrinos in the process $pp\to Z/h\toν_{4}{\barν_{4}}\to WμWμ$. We show that, depending on their masses, the simultaneous discovery of both the Higgs boson and the heavy neutrinos is probable at early stages of LHC operation. Results are presented for both Majorana and Dirac type fourth family neutrinos.
The fate of R-parity is one of the central issues in the minimal supersymmetric standard model (MSSM). Gauged $B-L$ symmetry provides a natural framework for addressing this question. Recently, it was pointed out that the minimal such theory does not need any additional Higgs if the $B-L$ breaking is achieved through the VEVs of right-handed sneutrinos, which ties the new physics scale to the scale of the MSSM. We show here that this immediately leads to an important prediction of two light sterile neutrinos, which can play a significant role in the BBN and neutrino oscillations. We also discu…
We study a model with $U(1)$ gauged lepton number symmetry in which the active neutrino masses are generated at two-loop level through the spontaneous breaking of the lepton number symmetry. To cancel gauge anomalies some exotic leptons are introduced that also play an important role in generating neutrino masses and the lightest neutral one can be a dark matter candidate. We discuss a phenomenology of the neutral fermion sector including dark matter, lepton flavor violations, and an extra neutral gauge boson $Z'$ that can be tested by $e^+ e^-$ collision at the International Linear Collider (…
We analyze the power of the Tevatron dataset to exclude or discover fourth generation neutrinos. In a general framework, one can have mixed left- and right-handed neutrinos, with Dirac and Majorana neutrinos as extreme cases. We demonstrate that a single Tevatron experiment can make powerful statements across the entire mixing space, extending LEP's mass limits of 60-80 GeV up to 150-175 GeV, depending on the mixing.
We investigate the lepton flavor violation decays, $τ\to μγ$, $τ\to eγ$ and $μ\to eγ$, in the framwork of a squential fourth generation model with a heavy fourth neutrino, $ν'$. Using the recent experimental bounds, we can obtain the constraints of the $4\times 4$ leptonic mixing matrix element factors, $V_{1ν'},V_{2ν'}$ and $V_{3ν'}$. We find that LFV decays can give strigent costraints on the parameter space of the 4th neutrino mass $m_{ν'}$.
We study neutrino mass generation in models with four chiral families of leptons and quarks and four right handed neutrinos. Generically, in these models there are three different contributions to the light neutrino masses: the usual see-saw contribution, the tree-level contribution due to mixing of light neutrinos with neutrino of the fourth generation, and the two loop contribution due to the Majorana mass term of the fourth neutrino. We study properties of these contributions and their experimental bounds. The regions of the parameters (mixings of the fourth neutrino, masses of RH neutrino …
