Daiji Kimura, Kang Young Lee, Takuya Morozumi, Keita Nakagawa
CP violation of the charged lepton sector has not been found yet. Tau is a unique charged lepton which can decay into hadrons. In this talk, we argue what kind of new physics can be studied with CP violation of tau lepton decays. We also disucuss how to handle hadronic final state interactions for a prediction of the direct CP violation.
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We discuss the ways to find CP violation in the decay of $τ^\pm\to ν_τ+ 3π$ from unpolarized as well as polarized $τ^\pm$.
Lepton flavor violation in tau and mu processes is studied in the littlest Higgs model with T-parity. We consider various asymmetries defined in polarized tau and mu decays. Correlations among branching ratios and asymmetries are shown in the following lepton flavor violation processes: mu+ --> e+ gamma, mu+ --> e+ e+ e-, mu- A --> e- A (A = Al, Ti, Au and Pb), tau+ --> mu+ gamma, tau+ --> mu+ mu+ mu-, tau+ --> mu+ e+ e-, tau+ --> mu+ P (P = pi0, eta and eta'), tau+ --> mu+ V (V = rho0, omega and phi), tau+ --> e+ gamma, tau+ --> e+ e+ e-, tau+ --> e+ mu+ mu-, tau+ --> e+ P, tau+ --> e+ V, tau…
We re-examine CP violation in the Delta S = 0 decays tau -> N pi nu_tau (N=2,3,4). We assume that the new physics (NP) is a charged Higgs. We show that there is no NP contribution to tau -> pi pi nu_tau, which means that no CP violation is expected in this decay. On the other hand, NP can contribute to tau -> N pi nu_tau (N=3,4). These are dominated by the intermediate resonant decays tau -> omega pi nu_tau, tau -> rho pi nu_tau and tau -> a_1 pi nu_tau. We show that the only sizeable CP-violating effects which are possible are in tau -> a_1 pi nu_tau -> 4 pi nu_tau (polarization-dependent rat…
We examine CP violation in the Delta S=0 decays tau -> omega pi nu_tau and tau -> a_1 pi nu_tau and the Delta S=1 decay tau -> K pi pi nu_tau. We assume that the new physics is a charged Higgs. We show that sizeable CP-violating effects are possible in tau -> a_1 pi nu_tau (polarization-dependent rate asymmetry) and tau -> omega pi nu_ tau (triple-product asymmetry). The Delta S=1 decay tau -> K pi pi nu_tau can proceed via several resonances. We construct two modified rate asymmetries and a triple product asymmetry for this decay and discuss the potential sensitivities of these asymmetries.
We analyze the CP violation in the semileptonic | ΔS|=1 tau-decays in supersymmetric extensions of the standard model (SM) with R parity violating term. We show that the CP asymmetry of tau-decay is enhanced significantly and the current experimental limits obtained by CLEO collaborations can be easily accommodated. We argue that observing CP violation in semi leptonic tau-decay would be a clear evidence for R-parity violating SUSY extension of the SM.
This paper has been withdrawn by the authors due to the crucial wrong assumption following Eq. 9.
We systematically investigate the possibility of finding CP/T violation in the $τ$ sector at Tau-Charm Factory. CP/T violation may occur at $τ$ pair production process, expressed as electric dipole moment, and at $tau$ decay processes. By assuming that electric dipole moment as large as $10^{-19}$e-cm and CP/T violation effect orignating from $τ$ decay as large as $10^{-3}$ are observable at Tau-Charm Factory, we studied all the possible extensions of the SM which are relevent for generating CP/T violation in $τ$ sector. And we pointed there are a few kind of models, which are hopeful for gene…
With the help of a physically motivated ansatz, which is fitted to the data, we estimate the size of possible duality violations in hadronic tau decay. The result is that the uncertainty associated with these violations could impact the alpha_s determination from the total decay width at a level which we estimate to be δalpha_s(m_tau) \sim 0.003-0.010. Consequently, it cannot be neglected.
The leading order contribution to the direct CP asymmetry in tau^{+/-} -> K^{+/-} pi^0 nu_{tau} decay rates is evaluated within the Standard Model. The weak phase required for CP violation is introduced through an interesting mechanism involving second order weak interactions, which is also responsible for tiny violations of the Delta S= Delta Q rule in K_{l3} decays. The calculated CP asymmetry turns out to be of order 10^{-12}, leaving a large window for studying effects of non-standard sources of CP violation in this observable.
In supersymmetry with large tan(beta) the decays B0(B0bar) -> l+l- are dominated by the scalar and pseudoscalar Higgs penguin diagrams leading to strong enhancement of leptonic decay rates with potentially large CP asymmetries in the tau+tau- decay modes measurable in BELLE or BaBar experiments. The TAUOLA tau-lepton decay library supplemented by its universal interface can efficiently be used to search for B0(B0bar) -> tau+tau- decays, and to investigate how the CP asymmetry is reflected in realistic experimental observables.
We show a general form of neutrino mass matrix (M), whose matrix elements are denoted by M_{ij} (i.j=e, mu, tau) as flavor neutrino masses, that induces maximal CP violation as well as maximal atmospheric neutrino mixing. The masses of M_{mu mu}, M_{tau tau} and M_{mu tau}+sigma M_{ee} (sigma =\pm 1) turn out to be completely determined by M_{e mu} and M_{e tau} for given mixing angles. The appearance of CP violation is found to originate from the interference between the mu-tau symmetric part of M and its breaking part. If |M_{e mu}|=|M_{e tau}|, giving either M_{e mu}=-sigma e^{i theta} M_{e…
We consider the production of tau pairs by electron-positron colliding beams at the maximum cross section near the threshold. At this energy tau pairs are produced mostly in the s-wave which implies that the spin of the tau pairs are almost always pointing in the beam direction independent of the production angle. When both electrons and positrons are longitudinally polarized in the same direction, for example 90%, one can obtain tau pairs with 99% polarization in the direction of the polarization vectors of the incident beams. Tests of CP violation and study of the structure of weak interacti…
We discuss a preliminary study of the impact of duality violations on extractions from tau decay data of the D=6 VEVs which determine chiral limit Standard Model K-->pi pi matrix elements of the electroweak penguin operators.
Establishing CP violation in B0 (bar{B0}) --> l+ l- decays requires a measurement of polarization of the final lepton pair, or a precise determination of the B0 --> l+ l- and bar{B0} --> l+ l- rates. We first argue that if the amplitudes of these decays are dominated by the scalar and pseudoscalar Higgs penguin diagrams, as happens e.g. in supersymmetry with large tan(beta), the CP asymmetries depend practically on only one CP violating phase. This phase can be large, of the order of the CKM phase, leading to large CP asymmetries in the tau+ tau- decay channel of B0_d (bar{B0}_d) mesons, poten…
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.
Motivated by the strong experimental evidence of large nu_mu - nu_tau neutrino oscillations, we study existing constraints for related mu - tau flavor violation. Using a general bottom-up approach, we construct dimension-6 effective fermionic operators whose coefficients encode the scale of new physics associated with mu - tau flavor violation, which is a piece in the puzzle of the origin of neutrino oscillations. We survey existing experimental bounds on this scale, which arise mostly from tau and B decays. In many cases the new physics scale is constrained to be above a few TeV. We also disc…
Isospin violating signals in the tau -> 3 pi nu_tau decay mode are discussed. For the tau -> pi^- pi^- pi^+ nu_tau decay mode, isospin violation arises from the vector current contribution in the tau -> omega pi nu_tau decay with the subsequent isospin violating omega decay into pi^+ pi^-. We demonstrate that such effects may be observed in presently available data through the measurement of the interference effects of these vector current contributions with the dominating axial vector current, i.e. through a measurement of the structure functions W_F,W_G,W_H and W_I. In the case of the tau ->…
We point out that oscillation between the two scalar tau (stau) mass eigenstates can give rise to CP-violation if some parameters appearing in the stau or chargino/neutralino mass matrices are complex. If stau^+ and stau^- decay into different charginos or neutralinos, rate asymmetries as large as 20% are possible. If both staus decay directly into tau + LSP, CP-violation can in principle still be observed through an energy asymmetry of the tau decay products, but this asymmetry never exceeds the percent level. Even the rate asymmetries become small if the mass splitting between the two stau m…
CP violation in the spin-spin correlations in chargino production and subsequent two-body decay into a tau and a tau-sneutrino is studied at the ILC. From the normal polarisation of the tau, an asymmetry is defined to test the CP-violating phase of the higgsino mass parameter μ. Asymmetries of more than \pm70% are obtained, also in scenarios with heavy first and second generation sfermions. Bounds on the statistical significances of the CP asymmetries are estimated. As a result, the normal tau polarisation in the chargino decay is one of the most sensitive probes to constrain or measure the ph…
Supersymmetric (SUSY) theories include many new parameters, some of which are CP-violating. Assuming that SUSY is found at a future high-energy collider, we examine the decay stop2 -> stop1 tau- tau+ with an eye to obtaining information about the new CP phases. We show that there are two CP-violating asymmetries which can be large in some regions of the SUSY parameter space. These involve measuring one or both of the tau spins. These asymmetries are particularly sensitive to phi_At, the phase of the trilinear coupling A_t.
We study CPT and Lorentz violation in the tau-lepton sector of the Standard Model in the context of the Standard-Model Extension, described by a coefficient which is thus far unbounded by experiment. We show that any non-zero value of this coefficient implies that, for sufficiently large energies, standard-model fermions become unstable against decay due to the emission of a pair of tau-antitau leptons. We calculate the induced fermion energy-loss rate and we deduce the first limit on the Lorentz- and CPT-violating coefficient.
We calculate the CP-violating rate asymmetry of H^\pm decays into tau and neutrino at one loop in the MSSM with complex parameters. We find that the asymmetry is typically of the order of 10^-3, depending mainly on the phases of the trilinear coupling A_τand of the gaugino mass M_1.
In this work we study the consistency of a possible non-vanishing coupling $Hμτ$ of the order of $3.6\times 10^{-3}$ as pointed recently by the CMS and ATLAS collaborations, with measured lepton flavor violation processes involving quarkonium. We show that the most promising channel to confirm this excess is to look for the lepton flavor tau decay into a $f_0$ and $μ$ where the experimental limit could strongly improved with the new B factories as Belle II.
We show that the CP-violating dipole form factors of the tau lepton can be of the order of $α/π$ in units of the length scale set by the inverse $Z$ boson mass. We propose a few observables which are sensitive to these form factors at LEP2 and higher e^+e^- collision energies.
We compute the SUSY effective hamiltonian that describes the |ΔS|=1 semileptonic decays of tau leptons. We provide analytical expressions for supersymmetric contribution to tau --> u bar{s} nu_{tau} transition in mass insertion approximation. We show that SUSY contributions may enhance the CP asymmetry of tau --> K pi nu_{tau} decays by several orders of magnitude than the standard model expectations. However, the resulting asymmetry is still well below the current experimental limits obtained by CLEO collaborations. We emphasize that measuring CP rate asymmetry in this decay larger than 10^{-…
We study the prospects of discovering CP-violation in the production of tau-leptons in the reaction {e+e- --> tau+tau- at TESLA, an e+e- linear collider with center-of-mass energies of 500 or even 800 GeV. Non-vanishing expectation values of certain correlations between the momenta of the decay products of the two tau leptons would signalthe presence of CP-violation beyond the standard model. We study how longitudinal beam polarization of the electron and positron beams will enhance these correlations. We find that T-odd and T-even vector correlations are well suited for the measurements of th…
In a supersymmetric model with the lightest supersymmetric particle (LSP) $χ$ in the range of a few hundred MeV's, the decay $τ{\longrightarrow} μχχ$ is going to be allowed. We investigate the departure from tau-universality caused by this decay. It is found that the universality violation in this way can be greater than both non-universal electroweak radiative corrections and supersymmetric one-loop corrections over a considerable region of the parameter space allowed by experiments so far. Thus it suggests a method of constraining the parameter space with light LSP's using data from tau-fact…
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 calculate the leading isospin-violating and electromagnetic corrections for the decay tau -> pi^0 pi nu_tau at low energies. The corrections are small but relevant for the inclusion of tau decay data in the determination of hadronic vacuum polarization especially for the anomalous magnetic moment of the muon. We show that part of the systematic differences between the measured form factors in tau -> pi^0 pi nu_tau and e^+ e^- -> pi^+ pi^- is due to isospin violation .
We propose that leptonic CP violation arises from a breaking of the mu-tau exchange symmetry in the neutrino mass matrix which in turn is indicated by the near maximal atmospheric neutrino mixing and the near zero θ_{13}. We find that for the case of a normal hierarchy, present data already restricts the way CP violation may appear in the neutrino mass matrix and there is an interesting correlation between the mixing angle θ_{13}, the solar mixing angle θ_{12} and the Dirac CP phase. In the inverted hierarchy only θ_{13} and the Dirac phase are linked. We also discuss the impact of this kind o…
If CP is violated in any decay process involving leptons it will signify the existense of a new force (called the X boson) responsible for CP violation that may be the key to understanding matter-antimatter asymmetry in the universe. We discuss the signatures of CP violation in (1) the decay of tau lepton, and (2) the semileptonic decay of $π$, K, D, B and t particles by measuring the polarization of the charged lepton in the decay. We discuss how the coupling constants and their phases of the coupling of the X boson to 9 quark vertices and 3 lepton vertices can be obtained through 12 decay pr…
CP violation from physics beyond the Standard Model (SM) is investigated in the Cabbibo-suppressed decay $τ\to Kπν_τ$ with polarized $τ$ leptons, to which both the ${\rm J}^{P}=1^-$ resonance $K^*$ and the $ J^{P}=0^+$ resonance $K^*_0$ contribute. In addition to the CP-odd rate asymmetry, $τ$ polarization enables us to construct three additional CP-odd polarization asymmetries that can be enhanced due to the interference between the $K^*$ and $K^*_0$, and whose magnitudes depend crucially on the $K^*_0$ decay constant, $f_{K^*_0}$. Taking a QCD sum rule estimate of $f_{K^*_0}=45$ MeV and the …
We investigate a potential of discovering lepton flavor violation (LFV) at the Large Hadron Collider. A sizeable LFV in low energy supersymmetry can be induced by massive right-handed neutrinos, which can explain neutrino oscillations via the seesaw mechanism. We investigate a scenario where the distribution of an invariant mass of two hadronically decaying taus ($\tauh\tauh$) from $\schizero{2}$ decays is the same in events with or without LFV. We first develop a transfer function using this ditau mass distribution to model the shape of the non-LFV $\tauhμ$ invariant mass. We then show the fe…
We discuss the test of CP and CPT violation in $τ$ decay without using the polarized electron beam by comparing partial fractions of $τ^-$ and $τ^+$ decay into channels with strong final state interactions. For example, $Γ(τ^-\rarrow π^-+π^0+ν) \ne Γ(τ^+\rarrow π^++π^0+ν)$ signifies violation of CP. The optimum energy to investigatge CP violation in $τ$ decay is discussed. We conclude that this energy is a few MeV below $ψ(2s)$ in order to avoid the charm contribution and over abundance of hadrons at the $ψ(2s)$ peak.
CP violation at low energy is investigated at the tau electromagnetic vertex. High statistics at B factories, and on top of the Upsilon resonances, allows a detailed investigation of CP-odd observables related to the tau-pair production. The contribution of the tau electric dipole moment is considered in detail. We perform an analysis independent from the high energy data by means of correlation and linear spin observables at low energy. We show that different CP-odd asymmetries, associated to the normal-transverse and normal-longitudinal correlation terms can be measured at low energy acceler…
We consider sparticle decays that violate tau lepton number, motivated by neutrino oscillation data. We work in the context of the constrained minimal supersymmetric extension of the Standard Model (CMSSM), in which the different sleptons have identical masses at the GUT scale, and neutrino Dirac Yukawa couplings mix them. We find that the branching ratio for decay of the heavier neutralino chi_2 to chi + tau mu is enhanced when the LSP mass m_chi = m_stau_1, including the region of CMSSM parameter space where coannihilation keeps the relic chi density within the range preferred by cosmology. …
Present experimental datas have shown a 3.8$σ$ level discrepancy with the standard model in $\overline{B}\to D^{(*)}τ\barν_τ$. Some new physics models have been considered to explain this discrepancy possibly with new source of the CP violation. In this paper, we construct CP violating observables by using multi-pion decays in $B\to Dτν_τ$, and estimate sensitivity of these observables to generic CP violating operators. We also discuss possibilities of CP violation in leptoquark models and in 2HDM of type-III.
We consider the sneutrino resonance reaction l^+ l^- -> sneutrino -> tau^+ tau^- in the MSSM without R-parity. We introduce new CP-violating and CP-conserving tau-spin asymmetries which are generated already at the tree-level if there is sneutrino - sneutrino-bar mixing and that are forbidden in the SM. It is remarkable that these spin asymmetries can reach ~75% around resonance for a sneutrino mass splitting of Δm ~ Γand ~10% for a splitting as low as Δm ~ 0.1Γ, where Γis the sneutrino width. We show that they are easily detectable already at LEP2 so long as the beam energy is within ~10 GeV …
We study a new supersymmetric mechanism for lepton flavour violation in muon and tau decays and muon -> e conversion in nuclei, within a minimal extension of the MSSM with low-mass heavy singlet neutrinos and sneutrinos. We find that the decays mu -> e gamma, tau -> e gamma and tau -> mu gamma are forbidden in the supersymmetric limit of the theory, whereas other processes, such as mu -> eee, mu -> e conversion, tau -> eee and tau -> e mu mu, are allowed and can be dramatically enhanced several orders of magnitude above the observable level by potentially large neutrino Yukawa coupling effects…
The theoretically clean channel B+ -> tau+ nu shows a close to 3sigma discrepancy between the Standard Model prediction and the data. This in turn puts a strong constraint on the parameter space of a two-Higgs doublet model, including R-parity conserving supersymmetry. The constraint is so strong that it almost smells of fine-tuning. We show how the parameter space opens up with the introduction of suitable R-parity violating interactions, and release the tension between data and theory.
The most stringent bounds on the anomalous magnetic and electric dipole moments of the tau lepton was derived by Escribano and Massó[6] from the Z width at LEP in an effective lagrangian approach to the new physics. In this paper we point out that the higher dimensional operators introduced by Escribano and Massó not only modify the neutral currents of the tau lepton to Z gauge boson and the photon, but also induce lepton flavor violation (LFV). The size of the LFV effect depends crucially on the dynamics of the lepton mass generation. Assuming the lepton mass matrices in the form of an Fritzs…
We present two recent developments on lepton flavour violation in the MSSM. 1) The supersymmetric seesaw mechanism can be realized through the exchange of heavy SU(2)_W-triplet states, rather than `right-handed' neutrinos. In this scenario the ratio of the tau --> mu gamma (or tau --> e gamma) and mu --> e gamma rates are unambiguously predicted in terms of the low-energy neutrino parameters. 2) Lepton flavour violating decays of the Higgs bosons, (h, H, A) --> mu tau, are induced at one-loop level. The branching ratios can reach 10^{-4} for large tan(beta) and sizeable smuon-stau mixing. Inte…
We study lepton flavor violation (LFV) in tau decays induced by heavy Majorana neutrinos within two models: (I) the Standard Model with additional right-handed heavy Majorana neutrinos, i.e., a typical seesaw-type model; (II) the Standard Model with left-handed and right-handed neutral singlets, which are inspired by certain scenarios of SO(10)models and heterotic superstring models with E_6 symmetry. We calculate various LFV branching ratios and a T-odd asymmetry. The seesaw Model I predicts very small branching ratios for LFV processes in most of the parameter space, although in a very restr…
We discuss in detail signals for CP violation in the Higgs boson and tau-slepton sectors through the production processes $μ^+μ^- \to \tildeτ_i^- \tildeτ_j^+$, where $i,j=1,2$ label the two $τ$ slepton mass eigenstates in the minimal supersymmetric standard model. We assume that the soft breaking parameters of third generation sfermions contain CP violating phases, which induce CP violation in the Higgs sector through quantum corrections. We classify all the observables for probing CP violation in the Higgs boson and $τ$ slepton sectors. These observables depend on the initial muon beam polari…
Lepton flavor violation with tau leptons
本文综述了τ轻子味破坏的研究现状，强调被忽视的味破缺模式及核子衰变中的τ味破坏，并指出其重要性。
It has been pointed out recently that current low-energy constraints still allow for sizable flavor-changing decay rates of the 125 GeV boson into leptons, h -> tau ell (ell= e, mu). In this work we discuss the role of hadronic tau-lepton decays in probing lepton flavor violating couplings in the Higgs sector. At low energy, the effective Higgs coupling to gluons induced by heavy quarks contributes to hadronic tau decays, establishing a direct connection with the relevant process at the LHC, pp (gg)-> h -> tau ell. Semileptonic transitions like tau -> ell pi pi are sensitive to flavor-changing…
We discuss some issues arising in the search for CP violation in the decays Z -> tau+ tau- and Z -> b \bar b X. The form-factor and the effective Lagrangian approach to parametrize CP-violating effects are compared. We emphasize the interest to study both real and imaginary parts of CP-violating form factors like the weak dipole moment form factor d_tau^Z(m^2_Z) of the tau-lepton. We propose an 'optimal' way to search for CP violation when Z -> b \bar b X events have to be selected on a statistical basis from the total number of Z hadronic decays.
We perform a detailed analysis of several mu-tau lepton flavour violating (LFV) processes, namely tau --> mu X (X = gamma, e+ e-, mu+ mu-, rho, pi, eta, eta'), Z --> mu tau and Higgs boson decays into mu tau. First we present a model independent operator analysis relevant to such decays, then we explicitly compute the LFV operator coefficients [and (g_μ-2)] in a general unconstrained MSSM framework, allowing slepton mass matrices to have large mu-tau entries. We systematically study the role and the interplay of dipole and non-dipole operators, showing how the rates and the mutual correlations…
We discuss signals for CP-violation in $μ^+ μ^- \to \tilde τ_i^- \tilde τ_j^+$, where $i,j = 1,2$ label the two scalar $τ$ mass eigenstates. We assume that these reactions can proceed through the production and decay of the heavy neutral Higgs bosons present in supersymmetric models. CP-violation in the Higgs sector can be probed through a rate asymmetry even with unpolarized beams, while the CP-odd phase associated with the $\tilde τ$ mass matrix can be probed only if the polarization of at least one beam can be varied. These asymmetries might be ${\cal O}(1)$.
Assuming a minimal seesaw model with two heavy neutrinos (N), we examine effects of leptonic CP violation induced by approximate mu-tau symmetric interactions. As long as N is subject to the mu-tau symmetry, we can choose CP phases of Dirac mass terms without loss of generality in such a way that these phases arise from mu-tau symmetry breaking interactions. In the case that no phase is present in heavy neutrino mass terms, leptonic CP phases are controlled by two phases alpha and beta. The similar consideration is extended to N blind to the mu-tau symmetry. It is argued that N subject (blind)…
We study charged lepton flavour violation in low-scale seesaw models of minimal supergravity, which realize large neutrino Yukawa couplings thanks to approximate lepton-number symmetries. There are two dominant sources of lepton flavour violation in such models. The first source originates from the usual soft supersymmetry-breaking sector, whilst the second one is entirely supersymmetric and comes from the supersymmetric neutrino Yukawa sector. Within the framework of minimal supergravity, we consider both sources of lepton flavour violation, soft and supersymmetric, and calculate a number of …
We study direct CP violation of tau -> K pi(eta,eta')nu decays. By studying the forward and backward asymmetry, the interference of L=0 and L=1 amplitudes of the hadronic system can be extracted. By including the scalar and vector mesons into the chiral Lagrangian, we compute the form factors which correspond to L=0 and L=1 angular momentum state of the hadronic system. We include real and imaginary parts of the one loop corrections to the self-energies of the scalar and vector mesons. The direct CP violation of the forward and backward asymmetry is computed using a two Higgs doublet model in …
We first study the hadronic lepton flavor violating tau decays within the littlest Higgs model with T-parity (including one or two pseudoscalars, or a vector resonance). We consider the case where only T-odd particles and partner fermions contribute, and also its extension including Majorana neutrinos coming from an inverse seesaw. In both cases our mean values lie only one order of magnitude below current upper limits, strengthening the case of searching for these decays in the quest for new physics.
For flavor neutrino masses M^{PDG}_{ij} (i,j=e,mu,tau) compatible with the phase convention defined by Particle Data Group (PDG), if neutrino mixings are controlled by small corrections to those with sin(theta_{13})=0 denoted by sin(theta_{13})deltaM^{PDG}_{e tau} and sin(theta_{13})deltaM^{PDG}_{tau tau}, CP-violating Dirac phase delta{CP} is calculated by using these corrections. If possible neutrino mass hierarchies are taken into account, the main source of delta{CP} turns out to be deltaM_{e tau}^{PDG} except for the inverted mass hierarchy with {m}_1 approx -{m}_2, where {m}_i=m_ie^{-i v…
We calculate the leading isospin-violating and electromagnetic corrections for the decay tau --> pi^0 pi nu_tau at low energies. The corrections are small but relevant for the inclusion of tau decay data in the determination of hadronic vacuum polarization especially for the anomalous magnetic moment of the muon.
We point out that, in the left-right symmetric model of weak interaction, if $ν_τ$ mass is in the keV to MeV range, there is a strong correlation between rare decays such as $τ\rightarrow 3 μ, τ\rightarrow 3 e$ and the $ν_τ$ mass. In particular, we point out that a large range of $ν_τ$ masses are forbidden by the cosmological constraints on $m_{ν_τ}$ in combination with the present upper limits on these processes.
We study lepton flavor violation (LFV) associated with tau leptons in the framework of the two Higgs doublet model, in which LFV couplings are introduced as a deviation from Model II Yukawa interaction. Parameters of the model are constrained from experimental results and also from requirements of theoretical consistencies such as vacuum stability and perturbative unitarity. Current data for rare tau decays provide substantial upper limits on the LFV Yukawa couplings in the large $\tanβ$ region ($\tanβ\gtrsim 30 $), which are comparable with predictions in fundamental theories. Here $\tanβ$ is…
In this work, we study the lepton number violating tau decays via intermediate on-shell Majorana neutrinos $N_j$ into two scalar mesons and a lepton $τ^{\pm} \to M_1{}^{\pm} N_j \to M_1^{\pm} M_2^{\pm} \ell^{\mp}$. We calculate the Branching ratios $Br(τ^{\pm})$ and the CP asymmetry $(Γ(τ^+) - Γ(τ^-))/(Γ(τ^+) + Γ(τ^-))$ for such decays, in a scenario that contain at least two heavy Majorana neutrinos. The results show that the CP asymmetry is small, but becomes comparable with the branching ratio ${\rm Br}(τ^{\pm})$ when their mass difference is comparable with their decay width, $ΔM_N \sim Γ_…
New avenues for tau flavor violation
本文探讨了tau味违犯的新途径，关注非标准衰变通道及其理论动机。
Recent studies of novel four-body lepton number violating decays of $τ$ leptons and neutral $B$ mesons are summarized and updated. These decays are assumed to be enhanced by the exchange of resonant Majorana neutrinos. It is shown that the $τ^- \to π^+l^-l^-ν_τ$ decay channels, with $l=e$ or $μ$, can provide stronger constraints on the mixing vs. mass parameter space of resonant Majorana neutrinos than analogous three-body decays of charged $B$ mesons.
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