In the context of general Minimal Supersymmetric Standard Model (MSSM), new sources for Lepton Flavor Violation (LFV) as well as CP-violation appear. We show that in the presence of LFV sources, the electric dipole moment of the electron ($d_e$) can receive new contributions. In particular, $d_e$ can receive a significant contribution at one loop level from the phase of the trilinear $A$-term of the staus, $ϕ_{A_τ}$. We discuss how we can derive information on $ϕ_{A_τ}$ by combining the information on $d_e$ with that on the LFV decay modes of the $τ$ lepton. We then discuss if this approach can be considered as an alternative to the direct measurement of $ϕ_{A_τ}$ at ILC.
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.
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.
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…
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.
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.
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.
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.
We summarized our report on leptonic flavor violating Higgs decay into mu + tau under the scheme of a generic supersymmetric standard model without R parity. With known experimental constraints imposed, important combinations of R-parity violating parameters which can give notable branching ratios are listed.
We derive the upper bounds on certain products of R-parity- and lepton-flavor-violating couplings from the decays of the neutral $B$ meson into two charged leptons. These modes of $B^0$ decays can constrain the product combinations of the couplings with one or more heavy generation indices. We find that most of these bounds are stronger than the previous ones.
We study baryogenesis through lepton number violation in left-right symmetric models. In these models the lepton number and CP violating interactions of the triplet higgs scalars can give rise to lepton number asymmetry through non-equilibrium decays of the $SU(2)_L$ triplet higgs and the right handed neutrinos. This in turn generates baryon asymmetry during the electroweak anomalous processes.
In this paper we study lepton flavor violating semileptonic decays of heavy baryons in a framework of a model with large extra dimensions and a single generation . Resulting branching ratios for these decays mediated by Kaluza-Klein modes of photon and Z-boson are presented in a model-independent form.
We discuss the effects of lepton number violating interactions namely, R-parity violation and leptoquarks on top quark pair production at the upcoming $e^+ e^-$ linear colliders. Effects of SU(2) singlet, doublet and triplet leptoquark interactions are investigated. R-parity violating minimal supersymmetric standard model also allows certain kinds of lepton number violating interactions which are same as singlet leptoquarks with left-handed interactions. We have calculated the cross-section of $e^+ e^- \to t \bar t$ in presence of the above interactions. With conservative values of lepton numb…
In the supersymmetric model with local gauged baryon and lepton numbers(BLMSSM), the CP violating effects are considered to study the lepton electric dipole moment(EDM). The CP violating phases in BLMSSM are more than those in the standard model(SM) and can give large contributions. The analysis of the EDMs for the leptons $e,μ, τ$ is shown in this work. It is in favour of exploring the source of CP violation and probing the physics beyond SM.
We show that the predictions for lepton flavor violating decays, in the case of quasi-degenerate neutrinos, change drastically when we include in the computation the high-energy phases present in the matrix of neutrino Yukawa couplings.
Exotic Higgs decays are promising channels to discover new physics in the near future. We present a simple model with a new light scalar that couples to the Standard Model through a charged lepton-flavor violating interaction. This can yield exciting new signatures, such as $h \to e^+ e^+ μ^-μ^-$, that currently have no dedicated searches at the Large Hadron Collider. We discuss this model in detail, assess sensitivity from flavor constraints, explore current constraints from existing multi-lepton searches, and construct a new search strategy to optimally target these exotic, lepton-flavor vio…
We study the contribution of the tensor unparticle mediation to the branching ratios of the radiative lepton flavor violating decays and predict a restriction region for free parameters of the scenario by using experimental upper limits. We observe that the branching ratios of the radiative lepton flavor violating decays are sensitive to the fundamental mass scales of the scenario and to the scale dimension of antisymmetric tensor unparticle. We obtain a more restricted set for the free parameters in the case of the μ\rightarrow e γdecay
We present a study of charged lepton mass matrix diagonalization in R-parity violating SUSY. The case in which the bilinear couplings $μ_i$ have large values is given special attention.
We demonstrate the existence of model independent one-to-one correspondence relations between different lepton flavor violating processes (LFV). Applying the criterion of naturalness, based on the idea of "custodial symmetry", we show that all the LFV processes, independently of specific mechanisms behind them, but with the same external leptons, have a priori comparable amplitudes modulo their kinematics and involved form factors.
Many models for physics beyond the Standard Model predict lepton-flavour violating decays of charged leptons at a level which may become observable very soon. In the present paper we investigate the decays of a Tau into three charged leptons in a generic way, based on effective-field-theory methods, where the relevant operators are classified according to their chirality structure. We work out the decay distributions and discuss phenomenological implications.
The dimension-six CP-violating SU_L(2)\times U_Y(1) invariant operators involving the tau lepton are studied. The constraints from the available experimental data on tau dipole moments are derived. Under the current constraints, the induced CP-violating effects could possibly be observed in tau -> 3πν_τ at the future tau-charm factory.
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.
We predict the branching ratios of the lepton flavor violating Higgs decays H^0->e^{\pm} μ^{\pm}, H^0-> e^{\pm} τ^{\pm} and H^0->μ^{\pm} τ^{\pm} in the case that the lepton flavor violation is carried by the scalar unparticle mediation. We observe that their branching ratios are strongly sensitive to the unparticle scaling dimension and they can reach to the values of the order of $10^{-4}$, for the heavy lepton flavor case and for the small values of the scaling dimension.
A minimal particle content supersymmetric model with a discrete Z_3 symmetry, allowing lepton number violating terms, is studied. Within this model, the neutrino masses and mixing can be generated by lepton number violating couplings. Choosing parameters which correctly describe both the masses and mixing in the neutrino sector, we consider their repercussions in flavour violating radiative lepton decays, l --> l' gamma. Such decays have not been observed and, accordingly, soon to be improved, upper bounds on their branching ratios exist. We do not assume dominance of either the bilinear or tr…
We study the effects of dimension six effective operators on the flavour violating production and decay of leptons at the International Linear Collider. Analytic expressions for the cross sections, decay widths and asymmetries of all flavour changing processes will be presented, as well as an analysis of the feasibility of their observation at the ILC.
We report results obtained with the first complete event generator for electroweak baryon and lepton number violating interactions at supercolliders. We find that baryon number violation would be very difficult to establish, but lepton number violation can be seen provided at least a few hundred L violating events are available with good electron or muon identification in the energy range 10 GeV to 1 TeV.
We present the results of an extensive analysis of lepton flavour violating decays in the Littlest Higgs model with T-parity (LHT). As lepton flavour violation is highly suppressed in the Standard Model by small neutrino masses, the LHT effects turn out to be naturally huge and could be seen in the near future experiments.
We calculate the cross sections of the baryon and lepton number violating processes. The proper valley method enables us to calculate the multi-boson processes, which have the possibility to observation. The mass corrections of the gauge boson, Higgs particle and top quark are evaluated and the group integration and the phase space integration are performed analytically and numerically.
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 one-loop supersymmetric contributions to lepton-flavor violating $Z$ -boson decays in a fully left-right symmetric model. In addition to right-handed scalar neutrinos, the decays could receive important contributions from doubly-charged triplet Higgsinos which couple to leptons only. We find that the decay widths reach present experimental bounds and discuss mass constraints for the contributing supersymmetric partners.
The non-leptonic two body decays of D mesons are studied in the framework of an improved factorization approximation. The final state interaction effects are taken into account assuming them dominated by nearby resonances. The agreement with experimental data is quite good. CP-violating asymmetries are predicted.
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 forward-backward and the CP-violating asymmetries (both time-independent and time-dependent) in rare semileptonic and radiative leptonic B_{d,s}-decays and investigate the sensitivity of these asymmetries to the extensions of the Standard model.
We compute the lepton flavour violating couplings of Higgs bosons in the Minimal Supersymmetric Standard Model, and show that they can induce the decays (h,H,A) --> mu tau at non-negligible rates, for large tan(beta) and sizeable smuon-stau mixing. We also discuss the prospects for detecting such decays at LHC and other colliders, as well as the correlation with other flavour violating processes, such as tau --> mu gamma and tau --> 3 mu.
We discuss SUSY models in which renormalizable lepton number violating couplings hide the decay of the Higgs through h -> χ_1^0 + χ_1^0 followed by χ_1^0 -> τ+ 2 jets or χ_1^0 -> ν_τ+ 2 jets and also explain neutrino masses. This mechanism can be made compatible with gauge mediated SUSY breaking.
We predict the branching ratios of the lepton flavor violating Z boson decays Z\to e^{\pm} μ^{\pm}, Z\to e^{\pm} τ^{\pm} and Z\to μ^{\pm} τ^{\pm} in the case that the lepton flavor violation is carried by the scalar unparticle mediation. We observe that their BRs are strongly sensitive to the unparticle scaling dimension and the branching ratios can reach to the values of the order of 10^{-8}, for the heavy lepton flavor case, for the small values of the scaling dimension.
In the Standard Model minimally extended to include massive neutrinos, we compute the leading CP-violating zero temperature contributions to the one-loop effective action induced by integration of the leptons. Such contributions start at operators of dimension six and they are P even for Dirac neutrinos and P even or odd for Majorana neutrinos. Dimension four operators are allowed in the mixed Dirac-Majorana case. It is verified by explicit calculation that CP can be violated in two generation settings for Majorana neutrinos. Using different neutrino scenarios we give upper bounds for the coup…
We predict the branching ratios of the lepton flavor violating radion decays r -> e^{\pm} μ^{\pm}, r -> e^{\pm} τ^{\pm} and r ->μ^{\pm} τ^{\pm} in the framework of the Randall-Sundrum scenario that the lepton flavor violation is carried by the scalar unparticle mediation. We observe that their BRs are strongly sensitive to the unparticle scaling dimension and, for its small values, the branching ratios can reach to the values of the order of 10^{-8}, for the heavy lepton flavor case.
We propose a new idea to test a class of loop-induced neutrino mass mechanisms by searching for lepton number violating charged current processes with incident of a neutrino beam. The expected rates of these processes are estimated based on some theoretical assumptions. They turn out to be sizable so that detection of such processes could be possible at near detectors in future highly intense neutrino-beam facilities.
We perform a quantitative study of neutrino phenomenology in the framework of minimal supergravity (mSUGRA) with grand unified theory (GUT)-scale tri-linear lepton number violation. We show that only two non-zero GUT scale lepton number violating parameters and three charged lepton mixing angles are sufficient to account for current neutrino oscillation data. This allows collider studies to be performed in a manageable parameter space. We discuss some phenomenological consequences of the models, including tuning issues.
The electroweak unification group $ SU(2)_L\times SU(2)_R\times SU(2)_Y $ is proposed for the charged lepton flavor violating decays of the muon ($μ$) and tau ($τ$) leptons. The group $SU(2)_Y$ is in the lepton space. The left-handed leptons and anti-leptons are assigned to the fundamental representation $(2,2,\bar{2})$ of the semi-simple group. The gauge group $SU(2)_Y$ is spontaneously broken to $U(1)_{Y_1}$, where $Y_1=-L=\pm1$ is the hypercharge, by introducing a scalar multiplet $Σ$ which belongs to the triplet representation 3 of the $SU(2)_Y$ and is singlet under $SU(2)_L\times SU(2)_R$…
A Majorana type of the neutrino mass matrix induces a class of lepton number violating processes. Cross sections of these reactions are given in terms of the neutrino mass matrix element, and a semi-realistic event rate is estimated. These processes provide mass and mixing parameters not directly accessible by the neutrino oscillation experiments. If these processes are discovered with a larger rate than given here, it would imply a new physics of the lepton number violation not directly related to the Majorana neutrino mass, such as R-parity violating operators in SUSY models.
We provide a detailed analysis of the supersymmetric tri-lepton signals for sparticle searches at the Tevatron in the minimal supersymmetric standard model with general CP-violating phases but without flavor mixing among sfermions of different generation. The stringent experimental constraints on the CP-violating phases from the electron and neutron electric dipole moments are included in the analysis for two exemplary scenarios of the SUSY parameters; one with decoupled first two generation sfermions and the other with non-decoupled sfermions. In both scenarios, the production cross section a…
We calculate the possible CP violating asymmetries for LFV decays mu -> e gamma and tau -> mu gamma. Our predictions depend on the chosen new model independent contribution. The result of measurements of such asymmetries for these decays will open a new window to determine the physics beyond the SM.
We discuss lepton number violating processes in the context of long-baseline neutrino oscillations. We summarise and compare neutrino flavour oscillations in quantum mechanics and quantum field theory, both for standard oscillations and for those that violate lepton number. When the active neutrinos are Majorana in nature, the required helicity reversal gives a strong suppression by the neutrino mass over the energy, $(m_ν/E_ν)^{2}$. Instead, the presence of non-standard lepton number violating interactions incorporating right-handed lepton currents at production or detection alleviate the mas…
We study constraints on light and feebly interacting bosons with lepton flavor violation from electron beam dump experiments. Scalar, vector, and dipole interactions of the bosons are analyzed, respectively, and excluded regions from the searches for decays into electron-positron pairs are derived. It is found that parameter regions unconstrained by flavor violating decays of muon can be excluded using the results of the E137 experiment. We also discuss the impact of the search for flavor violating decays of the light bosons in electron beam dump experiments.
Parity violating left-right scattering asymmetries at future high energy e+e- and e-e- colliders are examined. The utility of two polarized beams for precision measurements is pointed out. Sensitivity to ``new'' short-distance physics is briefly discussed. Electroweak radiative corrections due to the running of sin^2(theta_W)(q^2) are exhibited.
In this talk, we investigate Lepton Flavor Violating (LFV) tau decay by R-Parity Violating (RPV) operators controlled by a non-Abelian discrete $Q_6$ family symmetry. We assume that only a family symmetry determines the whole flavor structure of a model, and the model indicates specific predictions of LFV tau decay processes by RPV operators. We predict $BR(τ\to 3e)/BR(τ\to 3 μ) \sim 4 m_μ^2/m_τ^2$ in a $Q_6$ family symmetric model.
We study the sensitivity of the existing MEG data to lepton flavor violating axion-like particles produced through $μ^+ \to e^+ a γ$ and estimate the discovery potential for the upcoming MEG II experiment in this channel. The MEG II signal efficiency can be improved significantly if a new trigger can be implemented in a dedicated run with a reduced beam intensity. This search would establish the world leading measurement in this channel with only 1 month of data taking.
We study lepton flavor violation in a class of supersymmetric models with light sgoldstino - scalar superpartner of Goldstone fermions responsible for spontaneous supersymmetry breaking. Sgoldstino couplings to the Standard Model (SM) fermions are determined by the MSSM soft terms and, in general, provide with flavor violation in this sector. Sgoldstino admixture to the lightest Higgs boson results in changes of its coupling constants and, in particular, leads to lepton flavor-violating decay $h\toτμ$ of the Higgs resonance. We discuss viability and phenomenological consequences of this scenar…
We investigate the prediction on the lepton phases in theories with a non trivial correlation between quark (CKM) and lepton (PMNS) mixing matrices. We show that the actual evidence, under the only assumption that the correlation matrix $V^M$ product of $CKM$ and $PMNS$ has a zero in the entry $(1,3)$, gives us a prediction for the three CP-violating invariants $J$, $S_1$, and $S_2$. A better determination of the lepton mixing angles will give a strong prediction of the CP-violating invariants in the lepton sector. These will be tested in the next generation experiments. To clarify how our pre…
We study the impact of the inverse seesaw mechanism on several low-energy flavour violating observables such as tau decaying to three muons in the context of the Minimal Supersymmetric Standard Model. As a consequence of the inverse seesaw, the contributions of the right-handed sneutrinos significantly enhance the Higgs-mediated penguin diagrams. We find that different flavour violating branching ratios can be enhanced by as much as two orders of magnitude. We also comment on the impact of the Higgs-mediated processes on the leptonic B-meson decays and on the Higgs flavour violating decays.
We study lepton flavor violating analogs of the photoelectric effect, with a final $μ$ or $τ$ instead of an electron: $γe\to μ$ and $γe\to τ$. On the basis of the general parametrization of the matrix element of the electromagnetic current we estimate the upper limits for the cross sections and event rates of these processes, imposed by the current experimental bounds on $μ\to e γ$ and $τ\to e γ$ decays.
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.
There is no guarantee that the violation of lepton number, assuming it exists, will primarily manifest itself in neutrinoless double beta decay ($0νββ$). Lepton-number violation and lepton-flavor violation may be related, and much-needed information regarding the physics that violates lepton number can be learned by exploring observables that violate lepton flavors other than electron flavor. One of the most promising observables is $μ^- \rightarrow e^+$ conversion, which can be explored by experiments that are specifically designed to search for $μ^- \rightarrow e^-$ conversion. We survey lep…
We investigate lepton-number-violating decays $K^\mp \rightarrow π^\pm l^\mp l^\mp$ in the presence of sterile neutrinos. We consider minimal interactions with Standard-Model fields through Yukawa couplings as well as higher-dimensional operators in the framework of the neutrino-extended Standard Model Effective Field Theory. We use $SU(3)$ chiral perturbation theory to match to mesonic interactions and compute the lepton-number-violating decay rate in terms of the neutrino masses and the Wilson coefficients of higher-dimensional operators. For neutrinos that can be produced on-shell, the deca…
