We explore the limits on lepton-flavor universality (LFU) violation in theories where the hierarchy problem is solved by means of a warped extra dimension. In those theories LFU violation, in fermion interaction with Kaluza-Klein modes of gauge bosons, is provided ab initio when different flavor of fermions are differently localized along the extra dimension. As this fact arises from the mass pattern of quarks and leptons, LFU violation is natural in this class of theories. We analyze the experimental data pointing towards LFU violation, as well as the most relevant electroweak and flavor observables, and the LFU tests in the $μ/e$ and $τ/μ$ sectors. We find agreement with $R_{K^{(\ast)}}$ and $R_{D^{(\ast)}}$ data at 95% CL, provided the third generation left-handed fermions are composite ($0.14 < c_{b_L} < 0.28$ and $0.27 < c_{τ_L} < 0.33$), and find the absolute limits $R_{K^{(\ast)}}\gtrsim 0.79$ and $R_{D^{(\ast)}}/R_{D^{(\ast)}}^{\rm SM}\lesssim 1.13$. Moreover we predict $\mathcal B( B\to Kν\barν)\gtrsim 1.14\times 10^{-5}$ at 95% CL, smaller than the present experimental upper bound but a few times larger than the Standard Model prediction.
A Model of Lepton Masses from a Warped Extra Dimension
为了解释非层次中微子混合角和在弯曲额外维的背景下轻子味违反过程的缺乏，需要引入体味对称性。基于A4非阿贝尔离散对称性，我们给出了一个简单的RS模型中轻子质量和混合的模型。这种选择的优点是：（i）自然出现的三-双极大的混合模式;（ii）在中性部门的树级味违反完全没有;（iii）味规范玻色子的情况下;（iv）层次的带电轻子质量解释通过波函数重叠。我们提出了最小的字段内容和对称性破缺模式，以获得成功的这种类型的模型。从电弱精密测量的界限允许KK质量尺度低至3 TeV。在这个模型中不存在树级轻子味破坏，而环诱导的μ-> e γ分支分数安全地低于实验界限。
Lepton-flavor universality violation in $R_K$ and $R_{D^{(*)}}$ from warped space
BaBar、LHCb和Belle合作组在过程$b\to s\ell\ell$（$\ell=μ,e$）和$b\to c \ell\barν_\ell$（$\ell=τ,μ,e$）中发现了一些异常，特别是在观测量$R_K$和$R_{D^{(\ast)}}$中，导致了可能的轻子味普适性违反。如果这些异常被证实，它们将不可避免地导致物理学超越标准模型。在本文中，我们试图容纳目前的异常在额外的维理论，解决的自然性问题的标准模型的手段与红外膜附近的一个强共形性破坏翘曲度规。如果左手底夸克和μ轻子在对偶理论中具有某种程度的复合性，那么$R_K$反常是可以接受的。这个理论与所有的电弱和味观测量是一致的，并且与卡鲁扎-克莱因电弱规范玻色子和胶子的所有直接搜索是一致的。费米子谱和费米子混合角可以用大多数基本右手底夸克、τ轻子和μ轻子重现。此外，$R_{D^{(\ast)}}$反常现象要求左手τ轻子具有很强的复合性，这与$g_{τ_L}^Z$耦合的实验数据相矛盾，可能除非在CKM矩阵的固定过程中引入某种程度的微调。
We show that the observed anomalies in the lepton sector can be explained in extensions of the Standard Model that are natural and, therefore, resolve the Higgs sector hierarchy problem. The scale of new physics is around the TeV and Technicolor-like theories are ideal candidate models.
Supersymmetric Grand Unification and Lepton Universality in K-> l νDecays
受CERN NA 62实验对K -> l ν衰变轻子普适性检验的改进前景的启发，我们研究了超对称模型中K -> l ν衰变轻子非普适性的预言.在这个过程中，μ-e普适性的违反可能源于右手slepton扇区的混合效应，这为大\tan β区域的超对称味道物理学提供了一个独特的窗口。在大统一尺度下，具有普适软超光速破缺项的最小统一方案将预测轻子普适性的破坏可以忽略不计。然而，轻子的非普适性可以在非最小的大统一模型中观察到，高维项对费米子质量有贡献，在这种情况下，高于GUT尺度的重整化效应可能会增强右手轻子之间的混合。这可能导致在具有高\tan β、大A项和小带电希格斯玻色子玻色子质量的参数空间的特定区域中，在K -> l ν衰变中可观察到轻子非普适性。在K -> l ν衰变中，可观测到的非普适性与大的BR值（τ-> e γ）相关。电子电偶极矩的实验上限可以与稀薄发生相调和，如果后者发生在相对较低的尺度上，这也将缓解宇宙学引力子问题。即使轻子的非普适性在不久的将来不会被发现，人们仍然可以获得对模型参数的重要约束，以及右手费米子和sfermion混合的未知方面。
In high energy exclusive processes involving leptons, QED corrections can be sensitive to infrared scales like the lepton mass and the soft photon energy cut, resulting in large logarithms that need to be resummed to all order in $α$. When considering the ratio of the exclusive processes between two different lepton flavors, the ratio $R$ can be expressed in terms of factorized functions in the decoupled leptonic sectors. While some of the functional terms cancel, there remain the large logarithms due to the lepton mass difference and the energy cut. This factorization process can be universal…
We discuss the current status of lepton flavour universality observables in semileptonic charged and neutral current $B$ meson decays. We recapitulate the current experimental situation. Assuming the current tensions with the SM are of beyond the Standard Model origin we present their implications for the effective theory couplings. Then we discuss general leptoquark models before finally focussing on the model with two scalar leptoquarks ($R_2$ and $S_3$) which have couplings connected by the underlying Grand Unified Theory framework. We present the viability of the model with regard to lepto…
Lepton Flavor Universality Violation (LFUV) in $b\rightarrow s l^+ l^-$ processes is investigated in the context of a 331 model. It is shown that in order to explain the experimentally observed deviations from the Standard Model in these FCNC transitions, a non-minimal version of the model has to be considered. We investigate the ability of this model in accomodating the model-independant scenarios currently favored by global fits.
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…
We present Standard Model predictions for lepton flavour universality ratios of inclusive $B\to X_{(c)} \ell \barν_\ell$. For the $\ell=μ,e$, these ratios are very close to unity as expected. For the $τ$ mode, we update the SM prediction for the branching ratio including power-corrections in the heavy-quark expansion up to $1/m_b^3$. These inclusive ratios serve as an important cross-check of the exclusive $B\to D^{(*)}\ell\barν_\ell$ modes, in which tensions exists between the predictions and measurements in those modes.
Implications of lepton flavor universality violations in B decays
目前对b->c tau nu和b->u tau nu跃迁的测量结果与标准模型对轻子味普适性的预测相差近4 σ。我们研究新的物理解释这种异常。一个有效场论分析表明，最小的味道违反模型不是首选的解释，但也尚未排除。考虑到一般的味违反，右-右矢量和右-左标量夸克流被确定为可行的候选者。我们讨论了两个希格斯双重模型，leptoquarks以及夸克和轻子复合明确的例子。最后，对LHC的搜索和未来的测量（超级）B-工厂的影响。
最近观测到的MNS混合矩阵的轻子混合角$θ_{13}$很好地结合在夸克和轻子扇区之间的普遍混合假设中。这个假设断言，在带电轻子对角基中，除了相元之外，上、下型夸克和轻中微子的所有其他质量矩阵都被同一个么正矩阵对角化。对于夸克混合矩阵$V_{CKM}$和轻子混合矩阵$U_{MNS}(δ)$，在唯象水平上表示为$V_{CKM}= U_{MNS}(δ^\prime)^\dagger P U_{MNS}(δ)$。这里，$P$是对角相位质量矩阵。$δ^\prime$是与MNS轻子混合矩阵中狄拉克CP破坏相位$δ=1.1π$（最佳拟合）略有不同的相位参数。
Lepton Flavor Universality Violation (LFUV) in $B$ decays in both neutral $b\rightarrow s l^+ l^-$ and charged $b\rightarrow cl\barν_{l}$ processes observed in the ratios $R_{K^{(*)}}$ and $R_{D^{(*)}}$ is investigated in the framework of a model based on the extended symmetry gauge $SU(3)_{C}\otimes SU(3)_{L}\otimes U(1)_{X}$ whose leptonic sector consists of five triplets. It is shown that in order to explain the experimentally observed deviations from the Standard Model in these flavor changing transitions, a non-minimal version of the model has to be considered. We investigate the ability …
Motivated by recent experimental measurements on flavour physics, in tension with Standard Model predictions, we perform an updated analysis of New Physics violating Lepton Flavour Universality, by using the effective Lagrangian approach and in the Z' and S_3 leptoquark models. We explicitly analyze the impact of considering complex Wilson coefficients in the analysis of B-anomalies, by performing a global fit of R_K and R_K*0 observables, together with ΔMs and A_CP^mix. The inclusion of complex couplings provides a slightly improved global fit, and a marginally improved ΔMs prediction.
In this talk I will present the work that we did in \cite{1}\cite{2}\cite{3}\cite{4}\cite{5} related to observed lepton universality violation by Babar, Belle and LHCb in R($D^{(*)}$) and $R_{K^{(*)}}$ as well as the reported deviation in muon (g-2) by BNL. We had shown that all these anomalies as well as Baryon-genesis, Dark-matter and small neutrino masses could be explained by introducing new exotic scalars, leptons and scalar-leptoquarks only. It turn out that some of these models have very peculiar signatures such as prediction of existence of heavy stable charged particle \cite{1}\cite{2…
The evidence for Lepton Flavour Universality (LFU) violation in semileptonic $B$-decays has been rising over the past few years. Relying on generic effective field theory (EFT) results, it has been shown that models addressing the $B$-anomalies necessarily lead, at one-loop, to deviations from LFU in $τ$ decays at the few per-mil level. Once a (renormalizable) UV model is specified, the leading-log EFT result receives finite corrections from the matching at the UV scale. We discuss such corrections in a motivated class of models for the B-anomalies, based on an extended $SU(4) \times SU(3) \ti…
Relaxing Constraints from Lepton Flavor Violation in 5D Flavorful Theories
我们提出了新的机制，改善的卡鲁扎-克莱因（KK）质量标度的约束带电轻子味破坏的标准模型（SM）的框架内传播的一个扭曲的额外的维度，特别是在模型占中微子数据。这些机制利用了扩展的五维（5D）电弱规范对称性[SU（2）_L x SU（2）_R x U（1）_X]，为了满足该框架中的电弱精确测试，该规范对称性已经被强烈地激发。在这种对称性下，轻子表示的新选择（自然地）可以允许左手（LH）带电轻子的小混合角，同时允许它们的SU（2）_L伙伴的大混合角，即，LH中微子，中微子数据被占后者的混合。因此，在这些模型中，可以避免由在轻子带电电流中观察到的大混合角引起的带电轻子味违反的增强，该混合角存在于LH带电轻子和中微子混合角相似的表示的最小选择中。这个想法也可能是有用的抑制贡献B_{d, s}混合在这个框架中，为了抑制味道违反超伴侣（而不是从KK模式）在5D“美味超对称”模型。此外，较少的最小表示可以为费米子与Z的耦合转移提供监护保护，进而进一步抑制在扭曲的额外维度场景中来自树级Z交换的带电轻子味道违反。结果表明，即使在弯曲额外维的框架下，~O（3）TeV KK质量标度的5D味参数没有任何特殊结构，也能同时与带电轻子味破坏和中微子数据相一致。
We propose improved Lepton Flavor Universality (LFU) ratios in semileptonic $P\to V \ell \barν$ decays, when comparing $μ$ and $τ$ modes, that minimize the theoretical form-factor uncertainties. These optimized ratios are obtained with simple cuts or reweighting of the dilepton mass distributions, which imply a minimum loss of signal on the rare tauonic modes while maximizing the cancellation of theoretical uncertainties among the two modes. We illustrate the usefulness of these observables in $B_c\to J/ψ$, $B_c\to ψ(2S)$, $B\to D^\ast$ and $B_s\to D_s^\ast$ transitions, showing that in all ca…
331 models constitute an extension of the Standard Model (SM) obtained by enlarging the SM gauge group $SU(3)_\text{C}\times SU(2)_\text{L}\times U(1)_Y$ to the group $SU(3)_\text{C}\times SU(3)_\text{L}\times U(1)_X$. We investigate how a non-minimal 331 model may embed lepton flavour universality violating contributions to $b\to s\ell\ell$ processes without introducing lepton flavour violation, as suggested by the recent LHCb measurements of the ratios $R_K$ and $R_{K^*}$. We discuss the model-independent scenarios of New Physics in $b\to s\ell\ell$ currently favoured by the data that could …
We analyse the new physics implications of theoretically clean $b \to s$ observables in a model-independent approach and compare their coherence with the implications of other rare $B$-decays. A statistical comparison is done between the New Physics explanation and hadronic contributions as the source of the anomalies in angular observables of the $B\to K^*μμ$ decay. We make projections for future measurements that indicate that LHCb will be in the position to discover lepton non-universality via a single observable using the Run 3 data. The global fit of rare $B$-decays is given within a mult…
