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.
Quark and Lepton Flavour Physics in the Littlest Higgs Model with T-Parity
T宇称的最小希格斯模型（LHT）在夸克和轻子扇区都包含了新的味源和CP破坏。它们起源于新规范玻色子W_H、Z_H和A_H介导的普通费米子与镜像费米子的相互作用。在K_L -> pi ^0 nu {bar nu}、K^+ -> pi^+ nu {bar nu}、CP不对称性S_{psi phi}和轻子味违反衰变中，发现了与标准模型最惊人的偏离。特别是，后者的衰变提供了一个明确的区别LHT模型和MSSM。我们总结了最有趣的结果，三个广泛的分析味道物理的LHT模型。
Motivated by the latest neutrino oscillation data which is consistent with maximal atmospheric mixing and maximal leptonic CP violation, we review various results in $μτ$ symmetry, then include several new observations and clarifications, including identifying a new general form of neutrino mass matrix with $μτ$ symmetry. We then apply the new results to the neutrino mass matrix associated with the Littlest Seesaw model, and show that it approximately satisfies the new general form with $μτ$ symmetry, and that this is responsible for its approximate predictions of maximal atmospheric mixing an…
We propose a $μ-τ$ reflection symmetric Littlest Seesaw ($μτ$-LSS) model. In this model the two mass parameters of the LSS model are fixed to be in a special ratio by symmetry, so that the resulting neutrino mass matrix in the flavour basis (after the seesaw mechanism has been applied) satisfies $μ-τ$ reflection symmetry and has only one free adjustable parameter, namely an overall free mass scale. However the physical low energy predictions of the neutrino masses and lepton mixing angles and CP phases are subject to renormalisation group (RG) corrections, which introduces further parameters. …
We discuss spontaneously broken CP symmetry in two right-handed neutrino models based on the idea of having a {\it different residual flavour symmetry}, together with a {\it different residual CP symmetry}, associated with each of the two right-handed neutrinos. The charged lepton sector also has a {\it different residual flavour symmetry}. In such a {\it tri-direct CP approach}, we show that the combination of the three residual flavour and two residual CP symmetries provides a new way of fixing the parameters. To illustrate the approach, we revisit the Littlest Seesaw (LSS) model based on $S…
The flavour symmetry succeeds in explaining the current global fit results. Flavour-symmetry models can be tested by the future experiments that improve the precision of neutrino oscillation parameters, \textit{such as} the MuOn-decay MEdium baseline NeuTrino beam experiment (MOMENT). In this work, we consider tri-direct littlest seesaw (TDLS) models for a case study, and analyze how much MOMENT can extend our knowledge on the TDLS model. We find that measurements of $θ_{23}$ and $δ$ are crucial for MOMENT to exclude the model at more than $5σ$ confidence level, if the best fit values in the l…
The Littlest Higgs Model with T-parity (LHT) belongs to the simplest new physics scenarios with new sources of flavour and CP violation. We present a new analysis of quark observables in the LHT model in view of the oncoming flavour precision era. We use all available information on the CKM parameters, lattice QCD input and experimental data on quark flavour observables and corresponding theoretical calculations, taking into account new lower bounds on the symmetry breaking scale and the mirror quark masses from the LHC. We investigate by how much the branching ratios for a number of rare $K$ …
Charged Lepton Flavour Violation in Supersymmetric Low-Scale Seesaw Models
我们研究了最小超引力的低尺度跷跷板模型中的带电轻子味破坏，由于近似轻子数对称性，该模型实现了大的中微子汤川耦合。在这样的模型中有两个主要的轻子味破坏源。第一个来源来自通常的软超对称性破坏部门，而第二个是完全超对称的，来自超对称中微子汤川部门。在最小超引力的框架下，我们考虑了轻子味破坏的软源和超对称源，并计算了一些可能的轻子味破坏跃迁，如μ子和τ子的光子衰变，μ-> e γ，τ-> e γ和τ-> μ γ，它们的无中微子三体衰变，μ-> e e e，τ-> e e e e e，τ-> mu mu，τ-> e e μ和τ-> e μ μ以及核内的相干μ-> e转换。在考虑到目前的轻子味违反实验的排斥界限，我们得出的通用重马约拉纳质量尺度mN和轻到重中微子混合的理论限制。超对称低尺度跷跷板模型提供了不同的相关预测轻子味违反签名，这可能会发现在当前和预计的实验，如MEG，彗星/棱镜，Mu 2 e，超级BELLE和LHCb。
Learning about flavour structure from tau to ell gamma and mu to e gamma?
目前和即将进行的实验应该可以将辐射轻子衰变的灵敏度提高一个数量级。本文假设τ->（e，μ）γ衰变之一被观察到，并探讨了所需的新的风味耦合的结构和后果。在简单的模型（一个低尺度的跷跷板，leptoquarks），它示出的偶极顶点函数是成比例的产品的风味矩阵从拉格朗日（一个“Jarlskog样”不变），只要环粒子弱耦合到希格斯玻色子。其次，如果偶极顶点函数具有分层结构，则这可能意味着由于mu --> e gamma上的界限所暗示的“近似零”，因此只能观察到一些tau -->（e，mu）gamma模式。这种潜在的测试的层次结构的假设进行了讨论。
Sensitivity to the Higgs Sector of SUSY-Seesaw Models in the Lepton Flavour Violating tau-->mu f0(980) decay
本文研究了超对称-跷跷板模型下的轻子味破坏半轻子τ-> mu f0（980）衰变，其中MSSM谱被三个右手中微子及其超对称伴子扩展，并利用跷跷板机制产生中微子质量。我们估计了它通过希格斯介导通道tau--> mu H *--> mu f0（980）时的衰变率，其中H指CP偶MSSM希格斯玻色子玻色子h^0和H^0，轻子味破坏tau mu H顶点通过超对称环辐射产生。为了描述f0（980）介子，我们遵循手征约束的指导方针。作为我们的计算的一个含义，我们探讨了希格斯部门在这种衰变的敏感性，并将其与其他LFV τ衰变通道。我们对BR（tau--> mu f0（980））的预测与其目前非常具有竞争力的实验界的对抗，使我们提取了一些有趣的限制最相关的模型参数，特别是，tanbeta和m_{H^0}。
We propose a 6d model with a SUSY $SU(5)$ gauge symmetry. After compactification, it explains the origin of the $S_4$ Family Symmetry with CSD3 vacuum alignment, as well as $SU(5)$ breaking with doublet-triplet splitting. The model naturally accounts for all quark and lepton (including neutrino) masses and mixings, incorporating the highly predictive Littlest Seesaw structure. It spontaneously breaks CP symmetry, resulting in successful CP violation in the quark and lepton sectors, while solving the Strong CP problem. It also explains the Baryon Asymmetry of the Universe (BAU) through leptogen…
Motivated by flavour symmetry models, we construct theories based on a low-energy limit featuring lepton flavour triality that have the flavour-violating decays $τ^\pm \to μ^\pm μ^\pm e^\mp$ and $τ^\pm \to e^\pm e^\pm μ^\mp$ as the main phenomenological signatures of physics beyond the standard model. These decay modes are expected to be probed in the near future with increased sensitivity by the Belle II experiment at the SuperKEKB collider. The simple standard model extensions featured have doubly-charged scalars as the mediators of the above decay processes. The phenomenology of these exten…
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. Furthe…
Lepton Flavour Violation in a Supersymmetric Model with A4 Flavour Symmetry
在味对称群A4 XZ 3 XU（1）_{FN}下的超对称不变量模型中，计算了mu-> e γ，tau-> mu γ和tau -> e γ的分支比，其中近三双峰轻子混合是自然预言的.在小对称性破缺参数u（与反应器混合角theta_{13}同阶）的主导阶，我们发现分支比一般按u ^2标度。对mu -> e γ的分支比应用电流约束表明，对于小于1000 GeV的质量参数m_{SUSY}和m_{1/2}，在模型中u或tan（β）的小值是优选的。从正在进行的MEG实验预期的约束将提供一个严格的约束的参数空间的模型要么强制u约0.01和小tan（β）或m_{SUSY}和m_{1/2}以上1000 GeV。在flavon扇区中的普适软超对称破缺项的特殊情况下，振幅和分支比标度为u^4发生抵消，从而允许较小的slepton质量。预测tau -> mu γ和tau -> e γ的分支比与mu -> e γ的数量级相同，这排除了在不久的将来观察到这些tau衰变的可能性。
Within the Standard Model Effective Field Theory framework, with operators up to dimension 6, we perform a model-independent analysis of the lepton-flavour-violating processes involving tau leptons. Namely, we study hadronic tau decays and $\ell$--$τ$ conversion in nuclei, with $\ell = e,μ$. Based on available experimental limits, we establish constraints on the Wilson coefficients of the operators contributing to these processes. Our work paves the way to extract the related information from Belle II and foreseen future experiments.
Supersymmetric Seesaw without Singlet Neutrinos: Neutrino Masses and Lepton-Flavour Violation
我们考虑了由重SU（2）_W三重态而不是“右手”中微子单线态交换引起的超对称跷跷板机制产生中微子质量。我们表明，在这种情况下，在低能量的大气和太阳中微子实验中测试的中微子味结构是直接继承的中微子汤川耦合的三胞胎。这使我们能够预测τ--> μ γ（或τ--> e γ）和μ--> e γ衰变率的比率，根据低能中微子参数。此外，一旦模型被嵌入到大统一模型中，夸克味破坏就可以与轻子味破坏联系起来。
We study Lepton Flavour Violating hadron decays of the tau lepton within the Simplest Little Higgs model. Namely we consider $τ\rightarrow μ(P, V, PP)$ where $P$ and $V$ are short for a pseudoscalar and a vector meson. We find that, in the most positive scenarios, branching ratios for these processes are predicted to be, at least, four orders of magnitude smaller than present experimental bounds.
Within the Standard Model Effective Field Theory framework, with operators up to dimension 6, we perform a model-independent analysis of the lepton-flavour-violating processes involving tau leptons. Namely, we study hadronic tau decays and $\ell$-$τ$ conversion in nuclei ($\ell=e,μ$). Based on available experimental limits, we establish constraints on the Wilson coefficients of the operators contributing to these processes. The related information from Belle II and foreseen future experiments can be easily incorporated into the resulting framework.
