Source Of Lepton Flavor Violation Research Articles

Probing lepton flavor violating decays in MSSM with non-holomorphic soft terms

The Minimal Supersymmetric Standard Model (MSSM) can be extended to include non-holomorphic trilinear soft supersymmetry (SUSY) breaking interactions that may have distinct signatures. We consider non-vanishing off-diagonal entries of the coupling matrices associated with holomorphic (of MSSM) and non-holomorphic trilinear terms corresponding to sleptons with elements {A}_{ij}^l and {A}_{ij}^{prime l} . We first improve the MSSM charge breaking minima condition of the vacuum to include the off-diagonal entries {A}_{ij}^l (with i ≠ j). We further extend this analysis for non-holomorphic trilinear interactions. No other sources of lepton flavor violation like that from charged slepton matrices are considered. We constrain the interaction terms via the experimental limits of processes like charged leptons decaying with lepton flavor violation (LFV) and Higgs boson decaying to charged leptons with LFV. Apart from the leptonic decays we compute all the three neutral LFV Higgs boson decays of MSSM. We find that an analysis with non-vanishing {A}_{emu}^{prime } involving the first two generations of sleptons receives the dominant constraint from μ → eγ. On the other hand, {A}_{etau}^{prime } or {A}_{mu tau}^{prime } can be constrained from the CMS 13 TeV analysis giving limits to the respective Yukawa couplings via considering SM Higgs boson decaying into eτ or μτ final states. Contributions from Al is too little to have any significance compared to the large effect from {A}_{ij}^{prime l} .

Lepton flavor violation from SUSY with nonuniversal scalars

Right-handed neutrinos in supersymmetric models can act as the source of lepton flavor violation (LFV). We present experimental implications of lepton flavor-violating processes within a supersymmetric type-I seesaw framework in the three-extra-parameter non-universal Higgs model (NUHM3) for large (PMNS-like) and small (CKM-like) Yukawa mixing scenarios. We highlight LFV predictions for the natural (low $\Delta_{\rm EW}$) portion of parameter space. Our numerical analysis includes full 2-loop renormalization group running effects for the three neutrino masses and mass matrices. We show the projected discovery reach of various LFV experiments ($\textit{i.e.}$ Mu2e, Mu3e, MEG-II, Belle-II), and specify regions that have already been excluded by the LHC searches. Our results depend strongly on whether one has a normal sneutrino hierarchy (NSH) or an inverted sneutrino hierarchy (ISH). Natural SUSY with a NSH is already excluded by MEG-2013 results while large portions of ISH have been or will soon be tested. However, LFV processes from natural SUSY with small Yukawa mixing and an ISH seem below any projected sensitivities. A substantial amount of the remaining parameter space of models with large PMNS-like sneutrino mixing will be probed by Mu2e and MEG-II experiments whereas small, CKM-like Yukawa mixing predicts LFV decays which can hide from LFV experiments.

The full lepton flavor of the littlest Higgs model with T-parity

We re-examine lepton flavor violation (LFV) in the Littlest Higgs model with T-parity (LHT) including the full T-odd (non-singlet) lepton and Goldstone sectors. The heavy leptons induce two independent sources of LFV associated with the couplings necessary to give masses to the T-odd mirror fermions and to their partners in right-handed SO(5) multiplets, respectively. The latter, which have been neglected in the past, can be decoupled from gauge mediated processes but not from Higgs mediated ones and must therefore also be included in a general analysis of LFV in the LHT. We also further extend previous analyses by considering on-shell Z and Higgs LFV decays together with the LFV processes at low momentum transfer. We show that current experimental limits can probe the LHT parameter space up to global symmetry breaking scales f ∼ 10 TeV. For lower f values ≳ 1 TeV, μ − e transitions require the misalignment between the heavy and the Standard Model charged leptons to be ≲ 1%. Future LFV experiments using intense muon beams should be sensitive to misalignments below the per mille level. For τ LFV transitions, which could potentially be observed at Belle II and the LHC as well as future lepton colliders, we find that generically they can not discriminate between the LHT and supersymmetric models though in some regions of parameter space this may be possible.

Muon conversion to electron in nuclei within the BLMSSM

In a supersymmetric extension of the standard model with local gauged baryon and lepton numbers (BLMSSM), there are new sources for lepton flavor violation, because the right-handed neutrinos, new gauginos and Higgs are introduced. We investigate muon conversion to electron in nuclei within the BLMSSM in detail. The numerical results indicate that the mu rightarrow e conversion rates in nuclei within the BLMSSM can reach the experimental upper bound, which may be detected in the future experiments.

Lepton flavor changing Higgs decays in the littlest Higgs model with T-parity

We calculate loop induced lepton flavor violating Higgs decays in the Littlest Higgs model with T-parity. We find that a finite amplitude is obtained only when all contributions from the T-odd lepton sector are included. This is in contrast to lepton flavor violating processes mediated by gauge bosons where the partners of the right-handed mirror leptons can be decoupled from the spectrum. These partners are necessary to cancel the divergence in the Higgs mass introduced by the mirror leptons but are otherwise unnecessary and assumed to be decoupled in previous phenomenological studies. Further-more, as we emphasize, including the partner leptons in the spectrum also introduces a new source of lepton flavor violation via their couplings to the physical pseudo-Goldstone electroweak triplet scalar. Although this extra source also affects lepton flavor changing gauge transitions, it decouples from these amplitudes in the limit of heavy mass for the partner leptons. We find that the corresponding Higgs branching ratio into taus and muons can be as large as ∼ 0.2 × 10−6 for T-odd masses of the order a few TeV, a demanding challenge even for the high luminosity LHC.

Lepton flavor violation in the MSSM extension with gauged baryon and lepton numbers

In a supersymmetric extension of the standard model with local gauged baryon and lepton numbers (BLMSSM), there are new sources for lepton flavor violation, because the right-handed neutrinos and new gauginos are introduced. In BLMSSM, we study the charged lepton flavor violating processes $l_j\rightarrow l_i+\gamma$ and $l_j\rightarrow 3l_i$ in detail. The numerical results show that in some parameter space the branching ratios for charged lepton flavor violating processes can be large enough to be detected in the near future.

Erratum: Muon conversion to electron in nuclei within the μνSSM with a 125 GeV Higgs

Within framework of the $\mu$ from $\nu$ Supersymmetric Standard Model ($\mu\nu$SSM), three exotic right-handed neutrino superfields induce new sources for lepton-flavor violation. In this work, we investigate muon conversion to electron in nuclei within the $\mu\nu$SSM in detail. With a 125 GeV Higgs, the numerical results indicate that the $\mu-e$ conversion rates in nuclei within the $\mu\nu$SSM can reach the experimental upper bound, which could be detected with the future experimental sensitivities.

Muon conversion to electron in nuclei within the μνSSM with a 125 GeV Higgs

Within framework of the μ from ν Supersymmetric Standard Model (μνSSM), three exotic right-handed neutrino superfields induce new sources for lepton-flavor violation. In this work, we investigate muon conversion to electron in nuclei within the μνSSM in detail. With a 125GeV Higgs, the numerical results indicate that the μ − e conversion rates in nuclei within the μνSSM can reach the experimental upper bound, which could be detected with the future experimental sensitivities.

Lepton-flavor violation and [formula omitted] in the [formula omitted

Within framework of the μ from ν Supersymmetric Standard Model (μνSSM), exotic singlet right-handed neutrino superfields induce new sources for lepton-flavor violation. In this work, we investigate some lepton-flavor violating processes in detail in the μνSSM. The numerical results indicate that the branching ratios for lepton-flavor violating processes μ→eγ, τ→μγ and μ→3e can reach 10−12 when tanβ is large enough, which can be detected in near future. We also discuss the constraint on the relevant parameter space of the model from the muon anomalous magnetic dipole moment. In addition, from the scalars for the μνSSM we strictly separate the Goldstone bosons, which disappear in the physical gauge.

Charged lepton flavor violation in supersymmetric low-scale seesaw models

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 possible lepton-flavour-violating transitions, such as the photonic decays of muons and taus, mu -> e gamma, tau -> e gamma and tau -> mu gamma, their neutrinoless three-body decays, mu -> e e e, tau -> e e e, tau -> mu mu mu, tau -> e e mu and tau -> e mu mu, and the coherent mu -> e conversion in nuclei. After taking into account the exclusion bounds placed by present experiments of lepton flavour violation, we derive combined theoretical limits on the universal heavy Majorana mass scale mN and the light-to-heavy neutrino mixings. Supersymmetric low-scale seesaw models offer distinct correlated predictions for lepton-flavour-violating signatures, which might be discovered in current and projected experiments, such as MEG, COMET/PRISM, Mu2e, super-BELLE and LHCb.

Lepton flavour violation: physics potential of a Linear Collider

Abstract We revisit the potential of a Linear Collider concerning the study of lepton flavour violation, in view of new LHC bounds and of the (very) recent developments in lepton physics. Working in the framework of a type I supersymmetric seesaw, we evaluate the prospects of observing seesaw-induced lepton flavour violating final states of the type eμ plus missing energy, arising from e + e − and e − e − collisions. In both cases we address the potential background from standard model and supersymmetric charged currents. We also explore the possibility of electron and positron beam polarisation. The statistical significance of the signal, even in the absence of kinematical and/or detector cuts, renders the observation of such flavour violating events feasible over large regions of the parameter space. We further consider the μ − μ − + $ E_{{^{\text{miss}}}}^T $ final state in the e − e − beam option finding that, due to a very suppressed background, this process turns out to be a truly clear probe of a supersymmetric seesaw, assuming the latter to be the unique source of lepton flavour violation.

Neutralino dark matter and Higgs mediated lepton flavor violation in the minimal supersymmetric standard model

We consider the minimal supersymmetric standard model within a scenario of large $\tan\beta$ and heavy squarks and gluinos, with masses of the heavy neutral Higgs bosons below the TeV scale. We allow for the presence of a large, model independent, source of lepton flavor violation (LFV) in the slepton mass matrix in the $\tau-\mu$ sector by the mass insertion approximation. We constrain the parameter space using the $\tau$ LFV decays together with the $B$-mesons physics observables, the anomalous magnetic moment of the muon and the dark matter relic density. We further impose the exclusion limit on spin-independent neutralino-nucleon scattering from CDMS and the recent CDF limit from direct search of the heavy neutral Higgs at the TEVATRON. We re-examine the prospects for the detection of Higgs mediated LFV at LHC, at a photon collider and in LFV decays of the $\tau$ such as $\tau\to\mu\eta$, $\tau\to\mu\gamma$. We find rates probably too small to be observed at future experiments if models have to accommodate for the relic density measured by WMAP and explain the $(g-2)_{\mu}$ anomaly: better prospects are found if these two constraints are applied only as upper bounds. The spin-independent neutralino-nucleon cross section in the studied constrained parameter space is just below the present CDMS limit and the running XENON100 experiment will cover the region of the parameter space where the lightest neutralino has large gaugino-higgsino mixing.

Lepton flavor equilibration and leptogenesis

We study the role played in leptogenesis by the equilibration of lepton flavors, as could be induced in supersymmetric models by off diagonal soft breaking masses for the scalar lepton doublets m̃αβ, or more generically by new sources of lepton flavor violation. We show that if m̃αβ≳1 GeV and leptogenesis occurs below ∼ 100 TeV, dynamical flavor effects are irrelevant and leptogenesis is correctly described by a one-flavor Boltzmann equation. We also discuss spectator effects in low scale leptogenesis by taking into account various chemical equilibrium conditions enforced by the reactions that are in thermal equilibrium. We write down the Boltzmann equation for low scale supersymmetric leptogenesis that includes flavor and spectator effects in the presence of lepton flavor equilibration, and we show how it reduces to a particularly simple form.

Model discriminating power ofμ→econversion in nuclei

We assess the model discriminating power of a combined phenomenological analysis of mu -> e gamma and mu -> e conversion on different target nuclei, including the current hadronic uncertainties. We find that the theoretical uncertainties can be largely reduced by using input from lattice QCD and do not constitute a limiting factor in discriminating models where one or at most two underlying operators (dipole, scalar, vector) provide the dominant source of lepton flavor violation. Our results show that a realistic discrimination among underlying mechanisms requires a measurement of the ratio of conversion rates at the 5% level (two light nuclei) or at the 20% level (one light and one heavy nucleus). We have illustrated these main conclusions also in the context of a supersymmetric model.

μ→eγandτ→lγdecays in the fermion triplet seesaw model

In the framework of the seesaw models with triplets of fermions, we evaluate the decay rates of $\mu \to e \gamma$ and $\tau \to l \gamma$ transitions. We show that although, due to neutrino mass constraints, those rates are in general expected to be well under the present experimental limits, this is not necessarily always the case. Interestingly enough, the observation of one of those decays in planned experiments would nevertheless contradict bounds stemming from present experimental limits on the $\mu \to eee$ and $\tau \to 3 l$ decay rates. Such detection of radiative decays would therefore imply that there exist sources of lepton flavour violation not associated to triplet fermions.

Electron electric dipole moment from Lepton Flavor Violation

The general Minimal Supersymmetric Standard Model introduces new sources for Lepton Flavor Violation (LFV) as well as CP-violation. In this paper, we show that when both sources are present, the electric dipole moment of the electron, $d_e$, receives a contribution from the phase of the trilinear $A$-term of staus, $\phi_{A_\tau}$. For $\phi_{A_\tau}=\pi/2$, the value of $d_e$, depending on the ratios of the LFV mass elements, can range between zero and three orders of magnitude above the present bound. We show that the present bound on $d_e$ rules out a large portion of the CP-violating and the LFV parameter space which is consistent with the bounds on the LFV rare decays. We show that studying the correlation between $d_e$ and the P-odd asymmetry in $\tau \to e\gamma$ helps us to derive a more conclusive bound on $\phi_{A_\tau}$ We also discuss the possibility of cancelation among the contributions of different CP-violating phases to $d_e$.

Lepton flavor violation in the little Higgs model withTparity

Little Higgs models with T-parity may provide us with a new source of lepton flavor violation, as such, in this paper we consider the anomalous magnetic moment of the muon (g-2){sub {mu}} and the lepton flavor violating decays {mu}{yields}e{gamma} and {tau}{yields}{mu}{gamma} in the little Higgs model with T-parity [A. Goyal, hep-ph/0609095.]. Our results show that the present experimental constraints of {mu}{yields}e{gamma} are a much more useful tool for constraining the new sources of flavor violation, than from the other processes considered here, which are present in T-parity models.

Lepton flavour violation in realistic non-minimal supergravity models

Realistic effective supergravity models have a variety of sources of lepton flavour violation (LFV) which can drastically affect the predictions relative to the scenarios usually considered in the literature based on minimal supergravity and the supersymmetric see-saw mechanism. We investigate a string inspired effective supergravity model arising from intersecting D-branes supplemented by an additional U(1) family symmetry. In such theories the magnitude of the D-terms is predicted, and we calculate the branching ratios for μ→eγ and τ→μγ for different benchmark points designed to isolate the different non-minimal contributions. We find that the D-term contributions are generally dangerously large, but in certain cases such contributions can lead to a dramatic suppression of LFV rates, for example by cancelling the effect of the see-saw induced LFV in τ→μγ models with lop-sided textures. In the class of string models considered here we find the surprising result that the D-terms can sometimes serve to restore universality in the effective non-minimal supergravity theory.

Non-universal gaugino masses and the fate of μ→ eγ

We study charged lepton flavor violating processes in the context of supersymmetric models with non-universal gaugino masses. We consider the generic case of free gaugino masses, as well as specific models based on gaugino mediation and SU(5) GUTs. Under the assumption that the main source of lepton flavor violation resides in the off-diagonal elements of the left-handed slepton mass matrix, we show that BR( μ→ eγ) strongly depends on gaugino non-universality. When M 1 and M 2 have opposite signs, cancellations occurring between the neutralino and the chargino contributions can suppress, even completely, the branching ratio of charged lepton flavor violating decays. Moreover, we find that for M 3> M 2, M 1, BR( μ→ eγ) is an increasing function of M 3.

Lepton flavour violation from Yukawa operators, supergravity and the see-saw mechanism

We investigate the phenomenological impact of different sources of lepton flavour violation arising from realistic models based on supergravity mediated supersymmetry breaking with Yukawa operators. We discuss four distinct sources of lepton flavour violation in such models: minimum flavour violation, arising from neutrino masses and the see-saw mechanism with renormalisation group (RG) running; supergravity flavour violation due to the non-universal structure of the supergravity model; flavour violation due to Froggatt–Nielsen (FN) fields appearing in Yukawa operators developing supersymmetry breaking F-terms and contributing in an non-universal way to soft trilinear terms; and finally heavy Higgs flavour violation arising from the heavy Higgs fields used to break the unified gauge symmetry which also appear in Yukawa operators and behave analogously to the FN fields. In order to quantify the relative effects, we study a particular type I string inspired model based on a supersymmetric Pati–Salam model arising from intersecting D-branes, supplemented by a U(1) family symmetry.