The $CP$ violation in the neutrino transition electromagnetic dipole moment is discussed in the context of the Standard Model with an arbitrary number of right-handed singlet neutrinos. A full one-loop calculation of the neutrino electromagnetic form factors is performed in the Feynman gauge. A non-zero $CP$ asymmetry is generated by a required threshold condition for the neutrino masses along with non-vanishing $CP$ violating phases in the lepton flavour mixing matrix. We follow the paradiagm of $CP$ violation in neutrino oscillations to parametrise the flavour mixing contribution into a series of Jarlskog-like parameters. This formalism is then applied to a minimal seesaw model with two heavy right-handed neutrinos denoted $N_1$ and $N_2$. We observe that the $CP$ asymmetries for decays into light neutrinos $N\to νγ$ are extremely suppressed, maximally around $10^{-17}$. However the $CP$ asymmetry for $N_2 \to N_1 γ$ can reach of order unity. Even if the Dirac $CP$ phase $δ$ is the only source of $CP$ violation, a large $CP$ asymmetry around $10^{-5}$-$10^{-3}$ is comfortably achieved.
The scaling of lepton dipole moments with lepton mass
轻子和夸克的偶极矩是味空间中的矩阵，它可以像质量矩阵一样潜在地揭示理论的味结构。偶极矩阵的非对角元素导致变味衰变，如μ-> e γ，而对角元素的虚部则产生电偶极矩。本文分析了在标准模型以外的理论中轻子偶极矩随轻子质量的标度关系。虽然在许多模型中，偶极矩的尺度大致为轻子质量，但我们发现，存在简单的模型，其中偶极子的尺度为质量的立方或以其他方式。给出了一个立方标度的显式例子，它是由大角度中微子振荡数据独立激发的。我们的结果对电偶极矩e、μ和τ以及稀有衰变μ-> e γ和τ-> μγ的可观测性具有重要意义，并将在未来的几个实验中得到检验。
Pair production of tau leptons in two photon collision ${γγ\to τ^{+}τ}^{-}$ is studied at CLIC to test CP violating QED couplings of tau leptons. CP violating effects are investigated using tau pair spin correlations which are observed through the hadronic decay of each $τ$ into $πν$. Competitive bounds with previous works on the electric dipole moment from CP odd terms have been obtained.
Using the effective Lagrangian formalism, the anomalous magnetic and electric dipole moments of the tau-lepton in the $μ^{+}μ^{-} \rightarrow μ^{+}γ^{*} γ^{*} μ^{-}\rightarrow μ^{+}τ\barτμ^{-}$ process at the future muon colliders at the $\sqrt{s}=1.5, 3$ and $6$ TeV are investigated. In addition, the bounds at the $95\%$ confidence level on the dipole moments of the tau-lepton using different integrated luminosities are estimated. It is shown that the $μ^{+}μ^{-} \rightarrow μ^{+}γ^{*} γ^{*} μ^{-}\rightarrow μ^{+}τ\barτμ^{-}$ process leads to a remarkable improvement in the existing experimen…
We examine the lepton dipole moments in an extension of the Standard Model (SM), which contains vector-like leptons that couple only to the second-generation SM leptons. The model naturally leads to sizable contributions to the muon $g-2$ and the muon electric dipole moment (EDM). One feature of this model is that a sizable electron EDM is also induced at the two-loop level due to the existence of new vector-like leptons in the loops. We find parameter regions that can explain the muon $g-2$ anomaly and are also consistent with the experimental constraints coming from the electron EDM and the …
We study the constraints that can be placed on anomalous $τ$-lepton couplings at the LHC. We use an effective Lagrangian description for physics beyond the standard model which contains the $τ$-lepton anomalous magnetic moment, electric dipole moment and weak dipole moments in two operators of dimension six. We include in our study two additional operators of dimension eight that directly couple the $τ$-leptons to gluons and are therefore enhanced at the LHC. We consider the two main effects from these couplings: modifications to the Drell-Yan cross-section and to the $τ$-lepton pair productio…
Spin effects in the tau-lepton pair induced by anomalous magnetic and electric dipole moments
NSC Kharkiv Institute of Physics and Technology（哈尔科夫物理与技术国立科学中心）；V. N. Karazin Kharkiv National University（瓦西里·卡扎金哈尔科夫国立大学）；M. Smoluchowski Institute of Physics, Jagiellonian University（雅盖隆大学M.斯莫卢霍夫斯基物理研究所）
We address the impact of sterile fermions on charged lepton electric dipole moments. We show that in order to have a non-vanishing contribution to electric dipole moments, the minimal extension necessitates the addition of at least two sterile fermion states. Sterile neutrinos can give significant contributions to the charged lepton electric dipole moments if the masses of the non-degenerate sterile states are both above the electroweak scale. In addition, the Majorana nature of neutrinos is also important. Furthermore, we apply the computations of the electric dipole moments for the most mini…
The following proceedings contain a theory perspective on the flavor changing neutral current anomalies reported by LHCb on the ratios $B\to K^{(*)} μμ/B\to K^{(*)} ee$
We establish model independent bounds on the anomalous magnetic and electric dipole moments of the tau-lepton using the two-photon processes $γγ\to τ^+τ^-$ and $γγ\to τ^+τ^-γ$. We use ${\cal L}=10, 50, 100, 300, 500, 1000, 1500, 2000, 3000 \hspace{0.8mm}fb^{-1}$ of data collected with the future $e^+e^-$ linear collider such as the CLIC at $\sqrt{s}=380, 1500, 3000 \hspace{0.8mm}GeV$ and we consider systematic uncertainties of $δ_{sys}=0, 3, 5\hspace{1mm}\%$. Precise bounds at $95\%$ C. L. on the anomalous dipole moments to the tau-lepton $-0.00015\leq \tilde{a}_τ\leq 0.00017$ and $|\tilde{d}_…
We calculate the electric dipole moment for the electron and neutron in the framework of the 3-3-1 model with heavy charged leptons. We assume that the only source of $CP$ violation arises from a complex trilinear coupling constant and the three complex vacuum expectation values. However, two of the vacua phases are absorbed and the other two are equal up to a minus sign. Hence only one physical phase survives. In order to be compatible with the experimental data this phase has to be smaller than $10^{-6}$.
In this paper, using the Bestest Little Higgs Model (BLHM) we calculate at the one-loop level the contributions to the Anomalous Magnetic Dipole Moment (AMDM) and Anomalous Weak Magnetic Dipole Moment (AWMDM) of the tau-lepton. The implications from this model are study, emphasizing the contributions of the new physics induced by the new scalar and vector bosons of the BLHM: $S_i=H_0, A_0, ϕ^{0}, η^{0}, σ, H^{\pm}, ϕ^{\pm}, η^{\pm}$, and $V_i=Z', W'$, because these quantify the new physics. With these new contributions we estimated bounds on both the real and imaginary parts of the AMDM and AW…
Renormalization and two loop electroweak corrections to lepton anomalous dipole moments in the standard model and beyond (I): heavy fermion contributions
The inclusion of heavy neutral leptons to the Standard Model particle content could provide solutions to many open questions in particle physics and cosmology. The modification of the charged and neutral currents from active-sterile mixing of neutral leptons can provide novel signatures in Standard Model processes. We revisit the displaced vertex signature that could occur in collisions at the LHC via the decay of heavy neutral leptons with masses of a few GeV emphasizing the implications of flavor, kinematics, inclusive production and number of these extra neutral fermions. We study in partic…
We study the magnetic and weak magnetic dipole moments of charged leptons in the framework of the Two Higgs Doublet Model type III (THDM-III) with four zero textures. We first analyze the possibility that the discrepancy between the experimental measurements and the theoretical prediction of the muon anomalous magnetic dipole moment ($a_μ$) in the Standard Model (SM) can be explained in the context of the model and then find values for the parameters of the THDM-III: neutral and charged Higgs boson masses ($m_{H}$, $m_{H^{\pm}}$), mixing angles ($α, β$), CP-violating angles $θ_1,\,θ_2$ and an …
The article reviews the conditions for lepton-flavor conservation in leptonic interactions. The conditions are similar to those developed in the quark sector. For neutrinos the mass eigenstates are unitary superpositions of flavor states which together with small mass differences produce neutrino oscillations. A new property for neutrinos is the fact that their masses are very small suppressing their couplings to neutral scalar fields. The results are demonstrated in several models.
The magnetic moment of the $τ$ lepton is an interesting quantity that is potentially sensitive to physics beyond the Standard Model. Electroweak gauge invariance implies that a heavy new physics contribution to it takes the form of an operator which involves the Higgs boson, implying that rare Higgs decays are able to probe the same physics as $a_τ$. We examine the prospects for rare Higgs decays at future high energy lepton (electron or muon) colliders, and find that such a project collecting a few ab$^{-1}$ would be able to advance our understanding of this physics by roughly a factor of 10 …
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…
Lepton Dipole Moments in Supersymmetric Low-Scale Seesaw Models
研究了具有右手中微子超场的超对称低标度跷跷板模型中带电轻子的反常磁偶极矩和电偶极矩。我们考虑一个最小超引力的最小扩展框架，假设CP破坏起源于复杂的软超对称性破缺双线性和三线性耦合与右手sneutrino部门。我们给出了μ子反常磁矩和电子电偶极矩（EDM）的数值估计，它们是Majorana质量尺度mN和tan（β）等关键模型参数的函数。特别地，我们发现在这个模型中，单重中微子和超中微子对电子EDM的贡献很小，在10^{-27}-10 ^{-28} e cm量级，可以在现在和将来的实验中探测到.
