We study the lepton flavor violating processes of $τ^-\toμ^-PP$ decays with $PP=K^+K^-,K^0\bar{K}^0,π^+π^-,π^0π^0$ in the framework of two Higgs doublet model III by virtue of the Chiral Perturbation Theory. In this model, only three neutral Higgs bosons contribute to these decays. With the current experimental constraints, we show that (a) the contributions of $|λ_{uu(dd)}|$ term are very small for these four decays; (b) we get the correlation between $|λ_{ss}|$ and $|λ_{τμ}|$. For $|λ_{τμ}| \sim 10-400$, one has $|λ_{ss}|\sim 40-1$; (c) in the existing model parameter space, $Br(τ^- \to μ^- K^+K^-)$ could reach the order of ${\cal O}(10^{-8})$, but $Br(τ\to μ^- π^+π^-/π^0π^0)$ are too small to be observed.
The most general model independent expressions for the CP-violating asymmetry, longitudinal, transversal and normal polarizations of leptons are derived. Application of these general results to the concrete models such as Standard model and three different types of two Higgs doublet model is discussed.
In this paper we calculate the one loop contributions to the CP violating three gauge boson couplings in two-Higgs doublet and Left--Right symmetric models. In the two-Higgs doublet model only a P conserving and CP violating coupling is generated, and it can be large as $10^{-3}$. In the Left--Right symmetric model both P conserving and violating couplings are generated. Due to constraints on the $W_L$--$W_R$ mixing, these couplings are small.
We study the radiative lepton flavor violating l_1->l_2γdecays in the two Higgs doublet model with localized new Higgs doublet in the Randall Sundrum background. We estimate the contributions of the KK modes of new Higgs bosons and left (right) handed charged lepton doublets (singlets) on the branching ratios of the decays considered. We observe that there is an enhancement in the branching ratios with the addition of new Higgs boson and lepton KK modes.
We study the branching ratios of the lepton flavor violating processes μ-> e γ, τ-> e γand τ-> μγin the split fermion scenario, in the framework of the two Higgs doublet model. We observe that the branching ratios are relatively more sensitive to the compactification scale and the Gaussian widths of the leptons in the extra dimensions, for two extra dimensions and especially for the τ-> μγdecay.
We study the lepton electric dipole moments in the split fermion scenario, in the two Higgs doublet model, where the new Higgs scalars are localized around the origin in the extra dimension, with the help of the localizer field. We observe that the numerical value of the electron (muon, tau) electric dipole moment is at the order of the magnitude of 10^{-31} (10^{-24}, 10^{-22}) (e-cm) and this quantity is sensitive the new Higgs localization in the extra dimension.
We study the branching ratios of the lepton flavor violating processes μ-> eγ, τ-> eγand τ-> μγin the split fermion scenario, with the assumption that the new Higgs doublet is restricted to the 4D brane (thin bulk) in one and two extra dimensions, in the framework of the two Higgs doublet model. We observe that the branching ratios are sensitive to the location of the 4D brane and, in the second case, the width of the thin bulk, especially for the μ-> eγdecay.
We investigate a two Higgs doublet model with extra flavour depending $U(1)_X$ gauge symmetry where $Z'$ boson interactions can explain the Atomki anomaly by choosing appropriate charge assignment for the SM fermions. For parameter region explaining the Atomki anomaly we obtain light scalar boson with $\mathcal{O}(10)$ GeV mass, and we explore scalar sector to search for allowed parameter space. We then discuss anomalous magnetic dipole moment of muon and lepton flavour violating processes induced by Yukawa couplings of our model.
We calculate lepton flavor violating Z -> l^+ l^- decay in the framework of the general two Higgs Doublet model. In our calculations we used the constraints for the Yukawa couplings \barξ^{D}_{N,τe} and \barξ^{D}_{N,τμ} coming from the experimental result of muon electric dipole moment and upper limit of the BR(μ-> eγ). We observe that it is possible to reach the present experimental upper limits for the branching ratios of such Z decays in the model III.
We consider a SU(2)$ \otimes $U(1) gauge theory with many scalar doublets, but without fermions. We devise a systematic method of constructing quantities which are invariant under changes of basis of the scalar fields, but acquire a minus sign under a general CP transformation. Those quantities provide a basis-independent way of checking for the existence of CP violation.
We have explored properties of an extension of the Inert Doublet Model by the addition of an extra non-inert scalar doublet. The model offers a possibility of CP violation in the scalar sector and a candidate for the Dark Matter. Allowed regions in the plane spanned by the mass of the Dark-Matter particle and the lightest neutral Higgs particle have been identified, and constraints from direct and indirect-detection experiments have been studied. For favorable parameter regions one may observe long-lived charged particles produced at the LHC.
We studied the signatures at the LHC of the electroweak SU(2) lepton doublet which embeds a doubly charged lepton. The doubly charged lepton pair and single production rates, which are different from the triplet case, are studied and all the detectable decay modes are considered. We also applied the same kinematic cuts as in triplet case to reduce the background at LHC and the needed integrated luminosities to find the doubly charged leptons with different masses are analyzed. We also suggested a method to distinguish the exotic lepton doublet and triplet.
We predict the branching ratios of Z -> e^{\pm} μ^{\pm}, Z -> e^{\pm} τ^{\pm} and Z -> μ^{\pm} τ^{\pm} decays in the model III version of the two Higgs doublet model, with the inclusion of one and two spatial non-universal extra dimensions. We observe that the the branching ratios are not sensitive to a single extra dimension, however, this sensitivity is considerably large for two extra dimensions.
We study the neutral Higgs boson production at the CERN Large Hadron Collider (LHC) and the future $e^- e^+$ linear collider (ILC) in the two Higgs doublet model with CP violation. The CP-even and CP-odd scalars are mixed in this model, which affects the production processes of neutral Higgs boson. We examine the correlation of the Higgs production at LHC and ILC and provide a strategy to distinguish the model from the CP conserving model and to determine the parameters of the Higgs sector.
We study the decay width and CP-asymmetry of the inclusive process b--> s g g (g denotes gluon) in the three and two Higgs doublet models with complex Yukawa couplings. We analyse the dependencies of the differential decay width and CP-asymmetry to the s- quark energy E_s and CP violating parameter θ. We observe that there exist a considerable enhancement in the decay width and CP asymmetry is at the order of 10^{-2}. Further, it is possible to predict the sign of C_7^{eff} using the CP asymmetry.
We predict the branching ratios of Z-> e^{\pm} μ^{\pm}, Z-> e^{\pm} τ^{\pm} and Z-> μ^{\pm} τ^{\pm} decays in the framework of the 2HDM, in the split fermion scenario. We observe that the branching ratios are not sensitive to a single extra dimension, however, this sensitivity is considerably large for two extra dimensions.
Constraints on the whole spectrum of lepton flavor violating vertices are shown in the context of the standard two Higgs doublet model. The vertex involving the $e-τ$ mixing is much more constrained than the others, and the decays proportional to such vertex are usually very suppressed.
The decay width, forward-backward asymmetry and tau lepton longitudinal and transversal polarization for the exclusive (B -> K tau^+ tau^-) decay in a two Higgs doublet model are computed. It is shown that the forward-backward asymmetry and longitudinal polarization of the tau lepton are very effective tools for establishing new physics.
In the simplest examples of models with a discrete quark-lepton symmetry, an electroweak symmetry breaking sector with more than one Higgs doublet is necessary to obtain the correct mass relations between quarks and leptons. A two Higgs doublet model has flavour-nonconserving Yukawa couplings, which are proportional to the masses of the quark-lepton symmetric partners of the fermions. We describe how flavour changing leptonic decays can occur, with branching ratios not far beyond that currently measureable, enabling investigation of the phenomenology of such models.
Two-Higgs-Doublet Models (2HDMs) are amongst the simplest extensions of the Standard Model. Such models allow for tree-level CP Violation (CPV) in the Higgs sector. We analyse a class of CPV 2HDM (of Type-I) in which only one of the two Higgs doublets couples to quarks and leptons, avoiding dangerous Flavour Changing Neutral Currents. We provide an up to date and comprehensive analysis of the constraints and Large Hadron Collider (LHC) predictions of such a model. Of immediate interest to the LHC Run 2 is the golden channel where all three neutral Higgs bosons are observed to decay into gauge …
We study the branching ratios of the lepton flavor violating processes μ-> eγ, τ-> eγand τ-> μγby considering that the new Higgs scalars localize with Gaussian profile in the extra dimension. We see that the BRs of the LFV decays μ-> e γ, τ-> e γand τ-> μγare at the order of the magnitude of 10^{-12}, 10^{-16} and 10^{-12} in the considered range of the free parameters. These numerical values are slightly suppressed in the case that the localization points of new Higgs scalars are different than origin.
We consider the two Higgs doublet model (2HDM) along with a generation of vector-like lepton doublet and singlet to explain the observed discrepancies in the electron and muon anomalous magnetic moments. The type-X (lepton-specific) 2HDM can allow a light pseudo-scalar which is known to explain the muon anomalous magnetic moment at two-loop. Such a light particle induces a sizable negative contribution to the electron anomalous magnetic moment at one-loop in the presence of vector-like leptons evading all the experimental constraints.
We calculate the electric dipole moment of electron using the experimental result of muon electric dipole moment and upper limit of the BR(μ--> eγ) in the framework of the general two Higgs doublet model. Our prediction is 10^{-32} e-cm, which lies in the experimental current limits. Further, we obtain constraints for the Yukawa couplings \barξ^{D}_{N,τe} and \barξ^{D}_{N,τμ}. Finally we present an expression which connects the BR(τ\to μγ) and the electric dipole moment of τ-lepton and study the relation between these physical quantities.
In this paper, the lepton flavor violating $τ^- \to μ^-PP (PP=K^+K^-,K^0\bar{K}^0,π^+π^-,π^0π^0)$ decays are studied in the framework of the two Higgs doublet model(2HDM) III. We calculate these decays branching ratios and get the bounds of model parameter $|λ_{τμ}|$ from the experimental upper limits. Our results show that, the neutral Higgs bosons have tree-level contributions to these decays. Among these decays, the $τ^- \to μ^- K^+K^-$ decay is most sensitive to $|λ_{τμ}|$. In the existing parameters space, these decays could reach the measure capability of B factory. These processes can p…
We calculate the new physics effects to the branching ratios of the lepton flavor conserving decays Z -> l^+ l^- in the framework of the general two Higgs Doublet model. We predict the upper limits for the couplings |\barξ^{D}_{N,μτ}| and |\barξ^{D}_{N,ττ}| as 3\times 10^2 GeV and 1\times 10^2 GeV, respectively.
We have updated a recently proposed extension of the Inert Doublet Model. The extension amounts to the addition of an extra non-inert scalar doublet. The model thus offers a possibility of CP violation in the scalar sector and a candidate for the Dark Matter. The recent XENON100 direct-detection experiment excludes a considerable range of medium-low dark-matter masses, leaving only as viable very low masses of order 5-10 GeV, as well as the regions from \sim 60 to \sim 110 GeV, and above \sim 530 GeV. For favorable parameter regions one may observe related long-lived charged particles produced…
We study the production and decay of charged scalars, eta^\pm, in the context of a CP-Violating Inert-Doublet Model. The model is an extended version of the Inert Doublet Model with an extra Higgs doublet and provides new sources of CP violation and a dark matter candidate. As compared with the 2HDM, the particle spectrum contains two additional neutral scalars and a charged pair. These particles are subject to a Z_2 symmetry, but can be pair-produced in hadronic collisions. If a charged scalar is included in the pair, it decays to the stable dark-matter candidate (i.e., the lightest neutral i…
We predict the charged lepton electric dipole moments in the split fermion scenario in the framework of the two Higgs doublet model. We observe that the numerical value of the muon (tau) electric dipole moment is at the order of the magnitude of $10^{-22} (e-cm)$ ($10^{-20} (e-cm)$) and there is an enhancement in the case of two extra dimensions, especially for the tau lepton electric dipole moment.
Appreciable CP Asymmetries (~ 10%) can arise in the reaction e+ e- -> t bar-t Z already at TREE-LEVEL in models with two Higgs doublets. For a neutral Higgs particle, h, with a mass in the range 50 GeV < m_h < 400 GeV, it may be possible to detect a 2-3 sigma CP-odd effect in e+ e- -> t bar-t Z in ~ 1-2 years of running of a future high energy e+e- collider with c.m. energies of ~ 1-2 TeV and an integrated luminosity of 200-500 inverse fb.
Recently we presented the upgrade of our code BSMPT for the calculation of the electroweak phase transition (EWPT) to BSMPT v2 which now includes the computation of the baryon asymmetry of the universe (BAU) in the CP-violating 2-Higgs-Doublet Model (C2HDM). In this paper we use {\tt BSMPT v2} to investigate the size of the BAU that is obtained in the C2HDM with the two implemented approaches FH and VIA to derive the transport equations, by taking into account all relevant theoretical and experimental constraints. We identify similarities and differences in the results computed with the two me…
The implementation of maximally restrictive texture zeros in the leptonic sector is investigated in the context of two-Higgs-doublet models with Majorana neutrinos. After analyzing all maximally restrictive pairs of leptonic mass matrices with zero entries, we conclude that there are only four texture combinations that are compatible with observations at 3 sigma confidence level and can be implemented through Abelian symmetries in a two-Higgs-doublet model. The compatibility of these textures with current constraints on lepton-flavor-violating processes is also studied. The ultraviolet complet…
We investigate the radiative generation of lepton masses and mixing angles in the Standard Model extended by one right-handed neutrino and one extra Higgs doublet. We assume approximate rank-1 Yukawa couplings at a high energy scale and we calculate the one loop corrected charged lepton and neutrino mass matrices at the low energy scale. We find that quantum effects generate, for typical high energy parameters, a hierarchy between the muon and the tau mass, a hierarchy between the solar and the atmospheric mass splittings, and a pattern of leptonic mixing angles in qualitative agreement with e…
We discuss how charged-lepton masses can be induced in multi-Higgs doublet models (NHDMs) through renormalization group running of Yukawa couplings. Examples of electron and muon mass generation are presented within scenarios with two- and three-Higgs-doublet models. We also show that quantum corrections to the Yukawa couplings can be naturally of the same order as the tree-level values. The impact of such corrections in NHDMs with right-handed neutrinos is briefly commented.
There exist about $3.7σ$ positive and $2.4σ$ negative deviations in the muon and electron anomalous magnetic moments ($g-2$). Also, some ratios for lepton universality in $τ$ decays have almost $2σ$ deviations from the Standard Model. In this paper, we propose a lepton-specific inert two-Higgs-doublet model. After imposing all the relevant theoretical and experimental constraints, we show that these lepton anomalies can be explained simultaneously in many parameter spaces with $m_H > 200$ GeV and $m_A~(m_{H^\pm})> 500$ GeV for appropriate Yukawa couplings between leptons and inert Higgs. The k…
We study the current structure of the lepton flavor violating $τ\to3μ$ decay in Type-III 2HDM. This model has many coupling constants which affect this decay. We find that each coupling constant corresponds to the different final-state momenta distribution and vice versa. Using this fact, we suggest how to determine the current structure. We also find the upper limit $|η_{23}^Eη_{22}^E|<0.00022$ in the case that all Higgs bosons except for the lighter CP even neutral one $h^0$ are decoupled, $M_{h^0}=115$GeV and $\cosβ=1/\sqrt{2}$. The observable difference between the MSSM and type-III 2HDM i…
We study the effect of non-universal extra dimensions on the branching ratios of the lepton flavor violating processes μ\to eγand τ\to μγin the general two Higgs doublet model. We observe that these effects are small for a single extra dimension, however, in the case of two extra dimensions there is a considerable enhancement in the additional contributions.
We present a comprehensive update of the bounds on R-Parity violating supersymmetric couplings from lepton-flavour- and lepton-number-violating decay processes. We consider tau and mu decays as well as leptonic and semi-leptonic decays of mesons. We present several new bounds resulting from tau, eta and Kaon decays and correct some results in the literature concerning B-meson decays.
We predict the branching ratios of Z-> e^{\pm} μ^{\pm}, Z-> e^{\pm} τ^{\pm} and Z-> μ^{\pm} τ^{\pm} decays in the framework of the 2HDM with the inclusion of one and two extra dimensions, by considering that the new Higgs doublet is localized in the extra dimension with a Gaussian profile. We observe that their BRs are at the order of the magnitude of $10^{-10}$, $10^{-8}$ and $10^{-5}$ with the inclusion of a single extra dimension, in the given range of the free parameters. These numerical values are slightly suppressed in the case that the localization points of new Higgs scalars are differ…
Now the bounds on the lepton-flavor violating (LFV) decay modes of tau lepton are being improved by the Belle experiment in the KEK B factory. In this paper the LFV decay of tau lepton is discussed in the supersymmetric seesaw model, using the current neutrino oscillation data.
In the first part of this thesis, we consider an extension to the Standard Model composed by a Massive Vector Doublet under SU(2)L and a Left-handed Heavy Neutral Lepton. We study the production of these exotic leptons with a Same Flavor Opposite Sign standard lepton pair, and jets. We establish limits on the parameter space considering previous searches in this final state. After the limit definition, we study a modification on the event selection criteria in order to increase the possibility of probing these new particles at the Large Hadron Collider. Finally, we perform a parameter scan con…
Flavor violating Higgs signals, such as the top FCNC decay $t\to ch^0$ and the LFV Higgs decay $h^0\to τμ$, have been studied at the LHC. These signals can arise within the general Two-Higgs doublet model (THDM), where each Higgs doublet couples to all fermions types through Yukawa matrices $Y^f_1$ and $Y^f_2$. The Yukawa matrices can be assumed to have the same form or they could have different structures. In this paper we study the case when both $Y^f_1$ and $Y^f_2$ have completely different forms, but in such a way that they complement to produce a specific hermitian mass matrix. We find th…
We study the differential branching ratio, forward-backward asymmetry, CP-violating asymmetry, CP-violating asymmetry in the forward-backward asymmetry and polarization asymmetries of the final lepton in the B-> X_d \ell^+\ell^- decays in the context of a CP softly broken two Higgs doublet model. We analyze the dependencies of these observables on the model parameters by paying a special attention to the effects of neutral Higgs boson (NHB) exchanges and possible CP violating effects. We find that NHB effects are quite significant for the τmode. The above-mentioned observables seems to be prom…
We show that charged-lepton masses can be radiatively induced in multi-Higgs doublet models (NHDMs) through the renormalization group running of Yukawa couplings from high to low energies. Some extreme examples of electron and muon mass generation are discussed in the context of two and three Higgs doublet models. It is also shown that quantum corrections to the Yukawa couplings can be naturally of the same order as the tree-level values. We also comment on the implications of considering extensions of NHDMs in which right-handed neutrinos are added.
We propose a new mechanism to explain neutrino masses with lepton number conservation, in which the Dirac neutrino masses are generated at the two-loop level involving a dark matter candidate. In this model, branching ratios of lepton flavor violating decays of the Higgs boson can be much larger than those of lepton flavor violating decays of charged leptons. If lepton flavor violating decays of the Higgs boson are observed at future collider experiments without detecting lepton flavor violating decays of charged leptons, most of the models previously proposed for tiny neutrino masses are excl…
The radiative leptonic $B_{c}\toτ\bar{ν_τ}γ$ decay is analysed in context of 2HDM. It is shown that with large values of $tanβ$, the contributions of Model II to the decay rate exceeds considerably the Standard Model ones, while the contributions of Model I overlap with the Standard Model predictions.
Simple "unitarity inspired" relations between two- and three-body lepton flavor violating decays are noted and discussed. In the absence of cancellations, the existing strong bounds on $μ\to 3e$ and $ μ\to eγγ$ severly constrain two-body lepton flavor violating decays.
We study the radiative lepton flavor violating l_i -> l_jγdecays in the two Higgs doublet model, respecting the Randall Sundrum scenario and estimate the contributions of the KK modes of left (right) handed charged lepton doublets (singlets) on the branching ratios. We observe that the branching ratios are sensitive to the contributions of the charged lepton KK modes.
The type X (lepton-specific) two-Higgs-doublet model at large $\tanβ$ becomes leptophilic and thus allows a light pseudoscalar $A$ accommodating the observed muon $g-2$ deviation without conflicting with various hadronic constraints. On the other hand, it is strongly constrained by leptonic precision observables such as lepton universality test in the neutral and charged currents. Treating all the lepton universality data in a consistent way, we show how the current data constrain the parameter space of $m_A$ and $\tanβ$ for given degenerate masses of heavy Higgs bosons $H$ and $H^\pm$. While …
We analyze four-lepton contact interactions that lead to lepton flavor violating processes, with violation of individual family lepton number but total lepton number conserved. In an effective Lagrangian framework, the assumption of gauge invariance leads to relations among branching ratios and cross sections of lepton flavor violating processes. In this paper, we work out how to use these relations systematically. We also study the consequences of loop-induced processes.
Combining the multi-lepton searches at the LHC, we study the possibilities of accommodating the new data of muon and electron $g-2$ anomalies in the lepton-specific inert two-Higgs-doublet model. We take the heavy CP-even Higgs as the 125 GeV Higgs, and find the muon and electron $g-2$ anomalies can be explained simultaneously in the region of 5 GeV $< m_h<60$ GeV, 200 GeV $<m_A< 620$ GeV, 190 GeV $<m_{H^\pm}< 620$ GeV for appropriate Yukawa couplings between leptons and inert Higgs. Meanwhile, the model can give a better fit to the data of lepton universality in $τ$ decays than the SM. Furthe…
In this paper, the lepton flavor violating $τ^- \to μ^- V^0(V^0=ρ^0,ϕ,ω)$ decays are studied in the framework of the two Higgs doublet model(2HDM) III. We present a computation of the the $γ-$, $Z$ penguin and box diagrams contributions, and make an analysis of their impacts. Our results show that, among the $γ-$ penguins, the penguins with neutral Higgs in the loop are very larger than those with charged Higgs in the loop. We find that the model parameter $λ_{τμ}$ is tightly constrained at the order of $O(10^{-3})$ and the branching ratios of these decays are available at the experiment measu…
We study the feasibility of the Type-X two Higgs doublet model (THDM-X) at collider experiments. In the THDM-X, new Higgs bosons mostly decay into tau leptons in the wide range of the parameter space. Such scalar bosons are less constrained by current experimental data, because of the suppressed quark Yukawa interactions. We discuss a search strategy of the THDM-X with multi-tau lepton final states at International linear collider and Large Hadron Collider. By using the collinear approximation, we show that a four tau lepton signature (e^+e^- -> HA -> 4τ) can be a clean signal.
Supposing only Lorentz and the gauge invariances of the Lagrangian, we derive energy and angular distributions for $τ^\pm \to μ^\pm μ^\pm μ^\mp$ lepton flavor violating decay process. Using these results, we discuss methods to determine the parameters associated with the lepton flavor violating interactions.
The SM-like Higgs pair productions are discussed in the framework of the general CP-violating two-Higgs-doublet model, where we find the CP-violating mixing angles can be related to the Higgs self couplings. Therefore, the future experimental searches for Higgs boson pairs can be constrained by the improved precision of the electric dipole moment measurements. Based on a series constraints of the SM-like Higgs boson signal fits, the perturbative unitarity and stability bounds to the Higgs potential, and the most recent LHC searches for the heavy Higgs bosons, we suggest a set of benchmark mode…
We analyze the flavor changing decay $h\rightarrow μτ$ in the framework of a Two Higgs Doublet Model with a fourth generation of fermions (4G2HDM) which couples only to the heavy scalar doublet. We obtain that the respective branching ratio at one-loop level can reach values as high as $ 10^{-4}-10^{-6} $ for masses of $ 300 $ GeV to $ 1 $ TeV for the heavy leptons in the fourth family and the new heavy Higgs bosons. These radiative corrections are of the same order of magnitude as the tree level prediction of the 4G2HDM.
It is well known that a Weinberg dimension-5 operator for small neutrino masses can be realized at tree level in three types of renormalizable models: (i) the type-I seesaw mediated by fermion singlets, (ii) the type-II seesaw mediated by Higgs triplets, (iii) the type-III seesaw mediated by fermion triplets. We here point out such operator can be also induced at tree level by vector-like lepton doublets in association with unusual fermion singlets, Higgs triplets or fermion triplets. If these unusual fermion singlets, Higgs triplets or fermion triplets are heavy enough, their decays can gener…
The branching ratio, forward-backward asymmetry and CP violating asymmetry for (B -> X_d l^+ l^-) decay, in framework of the general two Higgs doublet model, with extra phase angle in the charged-Higgs-fermion coupling, are calculated. It is shown that studying the CP violating asymmetry is an efficient tool for establishing new physics.
We study the lepton flavor violating $μ^- \to e^{-}2γ$ decay induced by the mediation of heavy leptons such as the excited and fourth generation leptons. We have examined the effects of these leptons in the $μ^- \to e^{-}2γ$ decay. We have found that branching ratio of this decay is very sensitive to excited and fourth generation leptons. Furthermore, we have obtained the bounds on model parameters by using the current experimental limit of this decay.
Scalars with lepton number violating interactions decaying into lepton pairs, as those mediating the see-saw of type II, always include doubly-charged components. If these are observed at the LHC, their electro-weak quantum numbers can be determined through their leptonic decays in pair and single production.
Lepton flavor violating decays $Z \to μτ$ and $J/Ψ, Υ\to μτ$ are considered. It is shown that these decays can reach sizeable magnitudes if some specific lepton-flavor violating 4-fermion operators are generated by low scale quantum gravity effects, or by some other new physics at a TeV scale.
