A soft-wall warped extra dimension allows one to relax the tight constraints imposed by electroweak data in conventional Randall-Sundrum models. We investigate a setup, where the lepton flavour structure of the Standard Model is realised by split fermion locations. Bulk fermions with general locations are not analytically tractable in a soft-wall background, so we follow a numerical approach to perform the Kaluza-Klein reduction. Lepton flavour violation is induced by the exchange of Kaluza-Klein gauge bosons. We find that rates for processes such as muon-electron conversion are significantly reduced compared to hard-wall models, allowing for a Kaluza-Klein scale as low as 2 TeV. Accommodating small neutrino masses forces one to introduce a large hierarchy of scales into the model, making pressing the question of a suitable stabilisation mechanism.
Lepton Flavour Eigenstates do not Exist if Neutrinos are Massive: `Neutrino Oscillations' Reconsidered
如果中微子是有质量的，那么所有标准模型过程的振幅中都不存在“轻子味本征态”。测量的$Γ(π\to e ν)/Γ(π\to μν)$和MNS矩阵示出排除这种状态的存在。不同味中微子的非相干产生改变了通常假设轻子味本征态产生的振荡相位。新的预测可以通过比较π介子和K介子衰变中中微子的“$ν_μ$消失”，在长线基实验中得到检验。
A properly defined and suitably broken $U(2)$ flavour symmetry leads to successful quantitative relations between quark mass ratios and CKM angles. At the same time the intrinsic distinction introduced by $U(2)$ between the third and the first two families of quarks and leptons may support anomalies in charged and neutral current semi-leptonic $B$-decays of the kind tentatively observed in current flavour experiments. We show how this is possible by the exchange of the $(3,1)_{2/3}$ vector leptoquark in two $U(2)$-models with significantly different values of Lepton Flavour Universality violat…
Non-Standard neutrino Interactions (NSI) are vector contact interactions involving two neutrinos and two first generation fermions, which can affect neutrino propagation in matter. SU(2) gauge invariance suggests that NSI should be accompanied by more observable charged lepton contact interactions. However, these can be avoided at tree level in various ways. We focus on lepton flavour-changing NSI, suppose they are generated by New Physics heavier than $m_W$ that does not induce (charged) Lepton Flavour Violation (LFV) at tree level, and show that LFV is generated at one loop in most cases. Th…
在这篇评论文章中，我们强调的影响模型，将味对称性带电轻子味违反（LFV）的过程。味对称性提供了一个自然的方法来解释特殊的质量等级和混合模式的标准模型费米子。新的LFV源通常存在于标准模型之外的新物理中，并且味道对称性可以对LFV观测值做出独特的预测。他们的发现可以为区分味道对称性和新的物理场景提供重要信息。由于它们的高灵敏度，我们将专注于寻找低能LFV过程，如原子核中的μ-> e γ或μ-e转换，但我们也将强调LFV过程在LHC中的潜在影响。如果新的物理学在大型强子对撞机可以达到的尺度上发生，那么它们诱导的味道算子可能会被高度详细地探测。
Lepton flavour violation from right-handed neutrino thresholds
在超对称跷跷板机制下重新评价了带电轻子味破坏。本文指出，右手中微子的非平凡味结构，其影响迄今为止研究较少，可以引起显着的slepton味转变。在中微子Yukawa耦合为O（1）的前提下，右手中微子混合贡献可以构成$μ\rightarrow e γ$振幅的基础，它本身可能导致一个实验上可达到的速率，给出一个典型的低能s粒子谱。重点放在最近测得的轻子混合角$θ_{13}$以及轻子CP破坏相的关键作用。
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。
We provide a general classification of flavour symmetries according to their interplay with the proper Poincare' and gauge groups and to their linear or nonlinear action in field space. We focus on the lepton sector and we review the different types of symmetries describing neutrino masses and the lepton mixing matrix. For each type of symmetry we present several illustrative examples and we discuss specific strengths and limitations.
