Transforming a $μ$ to a $τ$, then the $τ$ to to an $e$, results in $μ\to e$. In an EFT framework, we explore the sensitivity of $μ\to e$ observables to products of $(μ\to τ)\times (τ\to e)$ interactions, and show that the exceptional sensitivity of upcoming $μ\to e$ experiments could allow to probe parameter space beyond the reach of upcoming $τ\to l$ searches in Higgs, $τ$ and $B$ decays. We describe the $τ\to l$ interactions as dimension six operators in the SM EFT, identify pairs of them giving interesting contributions to $μ\to e$ processes, and obtain the anomalous dimensions mixing those pairs into dimension eight $μ\to e$ operators. We find that $μ\to e$ processes are sensitive to $τ$ flavour-changing $B$ decays at rates comparable to current $B$ anomalies, but cannot reduce rates -- as appropriate in many current $B$ anomalies -- because they do not interfere with the SM.
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}。
In leptonic flavour models with discrete flavour symmetries, couplings between flavons and leptons can result in special flavour structures after they gain vacuum expectation values. At the same time, they can also contribute to the other lepton-flavour-violating processes. We study the flavon-induced LFV 3-body charged lepton decays and radiative decays and we take as example the $A_4$ discrete symmetry. In $A_4$ models, a $Z_3$ residual symmetry roughly holds in the charged lepton sector for the realisation of tri-bimaximal mixing at leading order. The only processes allowed by this symmetry…
We study the set of models in which the Standard Model symmetry is extended with the flavour group A4 and there are three copies of the Standard Model Higgs that transform as a triplet under this group. In this setup, new channels for flavour violating processes can be studied once the A4 representations of the fermions in the theory are given. We show that it is of great importance to take these constraints into account as they can put severe constraints on the viability of flavour models.
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。
The observation of neutrino oscillation as well as the recent experimental result on lepton flavor universality (LFU) violation in $B$ meson decays are indications of new physics beyond the Standard Model. Many theoretical models, which are introduced in the literature as an extension of SM to explain these observed deviations in LFU, lead to new kind of interactions so-called non-standard interaction (NSI) between the elementary particles. In this paper, we consider a model with an additional $Z'$ boson (which is quite successful in explaining the observed LFU anomalies) and analyze its effec…
We analyse various flavour changing processes like $t\to hu,hc$, $h\to τe,τμ$ as well as hadronic decays $h\to bs,bd$, in the framework of a class of two Higgs doublet models where there are flavour changing neutral scalar currents at tree level. These models have the remarkable feature of having these flavour-violating couplings entirely determined by the CKM and PMNS matrices as well as $\tanβ$. The flavour structure of these scalar currents results from a symmetry of the Lagrangian and therefore it is natural and stable under the renormalization group. We show that in some of the models the…
Dipole interactions encode a rich variety of phenomena, such as radiative decays and electric dipole moments in both quark and lepton sectors, which probe physics beyond the Standard Model up to very high energy scales; due to renormalization, non-dipole operators mix into dipole ones, thus possibly generating observable effects that can be investigated by those same phenomena. I consider four-fermion contact interactions for which the leading order mixing into dipoles happens at two-loops (i.e., when one-loop effects vanish) and for which this mixing can avoid small Yukawa couplings, and then…
We propose renormalizable models of new physics that can explain various anomalies observed in decays of B-mesons to electron and muon pairs. The new physics states couple to linear combinations of Standard Model fermions, yielding a pattern of flavour violation that gives a consistent fit to the gamut of flavour data. Accidental symmetries prevent contributions to baryon- and lepton-number-violating processes, as well as enforcing a loop suppression of new physics contributions to flavour violating processes. Data require that the new flavour-breaking couplings are largely aligned with the Yu…
A phenomenological study for determining the chirality structure in lepton-flavor-violating Higgs (hLFV) decays $h \to τμ$ at the LHC is presented. We estimate the effects of the $τ$ polarization in the analysis andthe importance of determining the relative visible momentum ratio $x$, and show the analysis with a collinear mass $m_{col1}$ by assuming one missing particle is appropriate. We find that the sensitivity would be generically affected up to $\pm$ $4-6$~\% in terms of the BR$(h\to τμ)$ upper bound, and show the altered bounds on the $(|y_{μτ}|, |y_{τμ}|)$ plane. We further study the b…
We suppose that the observed neutrino masses can be parametrised by a lepton number violating dimension-five operator, and calculate the mixing of double insertions of this operator into lepton flavour changing dimension-six operators of the standard model effective theory. This allows to predict the log-enhanced, but $m_ν^2$-suppressed lepton flavour violation that is generic to high-scale Majorana neutrino mass models. We also consider the Two Higgs Doublet Model, where the second Higgs allows the construction of three additional dimension-five operators, and evaluate the corresponding anoma…
It is pointed out that in a general class of flavour models one can identify certain universally present FCNC operators, induced by the exchange of heavy flavour messengers. Their coefficients depend on the rotation angles that connect flavour and fermion mass basis. The lower bounds on the messenger scale are derived using updated experimental constraints on the FCNC operators. The obtained bounds are different for different operators and in addition they depend on the chosen set of rotations. Given the sensitivity expected in the forthcoming experiments, the present analysis suggests interes…
We study the intersection of flavour and collider physics for Two-Higgs-Doublet models of Type I and II. Drawing from the flavour precision-LHC exotics search complementarity, we also provide a projection of the future sensitivity that can be achieved in light of currently available analyses. On the one hand, we find that the parameter space of the 2HDM can be explored significantly further with more data from the LHC with some complementarity with flavour physics. On the other hand, flavour physics results alongside their projections remain powerful tools to constrain the model space in regio…
The sensitivity of beam dump experiments to heavy neutral leptons depends on the relative strength of their couplings to individual lepton flavours in the Standard Model. We study the impact of present neutrino oscillation data on these couplings in the minimal type I seesaw model and find that it significantly constrains the allowed heavy neutrino flavour mixing patterns. We estimate the effect that the DUNE experiment will have on these predictions. We then discuss implication that this has for the sensitivity of the NA62 experiment when operated in the beam dump mode and provide sensitivity…
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…
Electric dipole moments and charged-lepton flavour-violating processes are extremely sensitive probes for new physics, complementary to direct searches as well as flavour-changing processes in the quark sector. Beyond the "smoking-gun" feature of a potential significant measurement, however, it is crucial to understand their implications for new physics models quantitatively. The corresponding multi-scale problem of relating the existing high-precision measurements to fundamental parameters can be approached model-independently to a large extent; however, care must be taken to include the unce…
Precision measurements of flavour observables provide powerful tests of many extensions of the Standard Model. This contribution covers a range of flavour measurements of $b\to s\ell^+\ell^-$ transitions, several of which are in tension with the Standard Model of particle physics, as well as their theoretical interpretation. The basics of the theoretical background are discussed before turning to the main question of the field: whether the anomalies can be explained by QCD effects or whether they may be indicators of effects beyond the Standard Model.
The forthcoming precision data on lepton flavour violating decays require precise and efficient calculations in New Physics models. In this article lepton flavour violating processes within the Minimal Supersymmetric Standard Model (MSSM) are calculated using the method based on the Flavour Expansion Theorem, a recently developed technique performing a purely algebraic mass-insertion expansion of the amplitudes. The expansion in both flavour-violating and flavour-conserving off-diagonal terms of sfermion and supersymmetric fermion mass matrices is considered. In this way the relevant processes…
We consider lepton flavour violating decays of the top quark, mediated by four-fermion operators. We compile constraints on a complete set of SU(3)*U(1)-invariant operators, arising from their loop contributions to rare decays and from HERA's single top search. The bounds on e-mu flavour change are more restrictive than l-tau; nonetheless the top could decay to a jet $+ e \barμ$ with a branching ratio of order $10^{-3}$. We estimate that the currently available LHC data (20 inverse-fb at 8 TeV) could be sensitive to $BR(t \to e \barμ$+ jet) $ \sim 6\times 10^{-5}$, and extrapolate that 100 inv…
In this paper, we study the hierarchy sensitivity of Protvino to ORCA (P2O) experiment in three flavour scenario as well as its sensitivity to non-standard interactions (NSI) in neutrino propagation. Because of the largest possible baseline length of 2595 km, P2O is expected to have strong sensitivity towards neutrino mass hierarchy and NSI parameters. In our study, we show that even though the number of appearance channel events for the minimal configuration of P2O are higher compared to DUNE, still the hierarchy sensitivity of P2O is less than DUNE because of large background events. Our res…
Violations of lepton flavour and CP in supersymmetric unified theories
由于大的顶夸克汤川耦合，超对称统一理论与软超对称破缺项在普朗克尺度预测轻子味和CP违反过程的显着率。在SU（5）和SO（10）两种理论中导出了低能理论的味破坏参数，并用于计算μ-> e γ的速率。比较了对μ-> e γ的搜索灵敏度与对原子中μ-> e转换、τ-> μ γ和电子电偶极矩的搜索灵敏度，表明对这些过程的实验搜索提供了一个非常有意义的超对称统一检验，特别是在SO（10）和SU（5）中。
Flavour-changing neutral currents are extremely rare processes in the standard model that can be sensitive to various new physics effects. The summary of the latest experimental results from the LHC experiments is given. Preliminary results of sensitivity studies for future colliders are also discussed.
