In the framework of the Standard Model we calculate the flavour non-universal correction for neutrino refraction in a neutrino background and verify a similar previous result for the case of ordinary-matter background. The dominant term arises at loop level and involves tau leptons circulating in the loop. These O(G_F m_tau^2) corrections to the tree-level potential provide the dominant refractive difference between nu_mu and nu_tau unless the medium contains mu or tau leptons. Our results affect the flavour evolution of dense neutrino gases and may be of interest for collective three-flavour oscillations of supernova neutrinos. We spell out explicitly how these non-universal neutrino-neutrino interactions enter the flavour oscillation equations.
Though models with the radiative neutrino mass generation are phenomenologically attractive, the complicated relationship between the flavour structure of additional Yukawa matrices and the neutrino mass matrix sometimes is a barrier to explore the models. We introduce a simple prescription to analyze the relation in a class of models with the asymmetric Yukawa structure. We then apply the treatment to the Zee-Babu model as a concrete example of the class and discuss the phenomenological consequences of the model. The combined studies among the neutrino physics, the lepton flavour violation, a…
We consider the one-loop radiative corrections to the light-neutrino mass matrix and their consequences for the predicted branching ratios of the five lepton-flavour-violating decays $\ell_1^- \to \ell_2^- \ell_3^+ \ell_3^-$ in a two-Higgs-doublet model furnished with the type-I seesaw mechanism and soft lepton-flavour violation. We find that the radiative corrections are very significant; they may alter the predicted branching ratios by several orders of magnitude and, in particular, they may help explain why $\mbox{BR}(μ^- \to e^- e^+ e^-)$ is strongly suppressed relative to the branching ra…
We study the phenomenology of a particular leptoquark extension of the Standard Model (SM), namely the doublet-singlet scalar leptoquark extension of the SM (DSL-SM). Besides generating Majorana mass for neutrinos, these leptoquarks contribute to muon and electron $(g-2)$ and various lepton flavour violating processes. Collider signatures of the benchmark points (BPs), consistent with the neutrino oscillation data, anomalous muon/electron magnetic moments, experimental bounds on the charged lepton flavour violation observables, etc., are studied at the LHC/FCC with centre-of-mass energies of 1…
Radiative corrections to $B \to D \ell ν_{\ell}$ decays can have an impact on predictions and measurements of the lepton universality ratios $\mathcal{R}(D^+)$ and $\mathcal{R}(D^0)$. These proceedings summarise a study on the comparison between recent calculations of soft-photon corrections on these ratios and the corrections simulated by the PHOTOS package. Also the impact of Coulomb interactions, not simulated in PHOTOS, is discussed. Using pseudo-experiments, the effect of high-energy photon emission is studied in an LHCb-like environment, showing a bias of up to 7\% on measurements of $\m…
Radiative corrections to $B \to D \ell ν_{\ell}$ decays may have an impact on predictions and measurements of the lepton flavour universality observables $\mathcal{R}(D^+)$ and $\mathcal{R}(D^0)$. In this paper, a comparison between recent calculations of the effect of soft-photon corrections on $\mathcal{R}(D^+)$ and $\mathcal{R}(D^0)$, and corrections generated by the widely used package PHOTOS is given. The impact of long-distance Coulomb interactions, which are not simulated in PHOTOS, is discussed. Furthermore, the effect of high-energy photon emission is studied through pseudo-experiment…
A framework based on a class of abelian gauge symmetries is proposed in which the masses of only the third generation quarks and leptons arise at the tree level. The fermions of the first and second families receive their masses through radiative corrections induced by the new gauge bosons in the loops. It is shown that the class of abelian symmetries which can viably implement this mechanism are flavour non-universal in nature. Taking the all-fermion generalization of the well-known leptonic $L_μ-L_τ$ and $L_e - L_μ$ symmetries, we construct an explicit renormalizable model based on two $U(1)…
We introduce two scalar leptoquarks, the SU$(2)_L$ isosinglet denoted $ϕ\sim(\mathbf{3}, \mathbf{1}, -1/3)$ and the isotriplet $φ\sim(\mathbf{3}, \mathbf{3}, -1/3)$, to explain observed deviations from the standard model in semi-leptonic $B$-meson decays. We explore the regions of parameter space in which this model accommodates the persistent tensions in the decay observables $R_{D^{(*)}}$, $R_{K^{(*)}}$, and angular observables in $b\to s μμ$ transitions. Additionally, we exploit the role of these exotics in existing models for one-loop neutrino mass generation derived from $ΔL=2$ effective …
By extending the Standard Model with singlet-doublet fermions and triplet scalars, all odd under a new $Z_2$ symmetry, we introduce a radiative seesaw model that can simultaneously account for dark matter, explain the existence of neutrino masses and allow for gauge coupling unification. We explore the viable parameter space of the model after imposing collider, Higgs mass, dark matter, neutrino mass and lepton flavour violation constraints. We find that dark matter in this model is fermionic for masses below about 1 TeV and scalar above and observe a high degree of complementarity between dir…
Neutrino Mixing and the Pattern of Supersymmetry Breaking
研究了标准模型超对称扩展中大$ν_μ- ν_τ$混合角对轻子味违反辐射跃迁的影响。过渡率计算到领先的顺序在$ε$，参数的特征的味道混合。详细讨论了预测速率的不确定性。对于具有模不变性的模型，分支比$BR(μ\to e γ)$大多超过实验上限。在辐射诱导味混合模型的预测范围包括上限，如果在轻子部门的汤川耦合大，汤川耦合统一的青睐。
Minimal Resonant Leptogenesis and Lepton Flavour Violation
我们讨论了最小的非超对称模型的共振leptogenesis，基于近似味对称。作为一个说明性的例子，我们考虑一个共振τ-leptogenesis模型，兼容的通用右手中微子质量在大统一体尺度，所需的重中微子质量分裂产生辐射。特别是，我们明确地证明，如何最小数量的三个重马约拉纳中微子是必要的，以获得成功的leptogenesis和实验可测试的速率轻子味违反的过程中，如μ--> e γ和μ--> e转换的核。
We propose a low-scale renormalizable trinification theory that successfully explains the flavor hierarchies and neutrino puzzle in the Standard Model (SM), as well as provides a dark matter candidate and also contains the necessary means for efficient leptogenesis. The proposed theory is based on the trinification $\SU{3}{C}\times \SU{3}{L}\times \SU{3}{R}$ gauge symmetry, which is supplemented with an additional flavor symmetry $\U{X}\times Z_{2}^{(1)} \times Z_{2}^{(2)}$. In the proposed model the top quark and the exotic fermions acquire tree-level masses, whereas the lighter SM charged fe…
This note reviews recent theoretical developments in the study of charged lepton flavour violation. The first part illustrates the status of precise next-to-leading order quantum electrodynamics calculations for the background of charged lepton flavour-violating processes, with a focus on the muonic "rare" and "radiative" decays. Phenomenological implications of these computations and their impact on present and future experiments will be discussed. The second part describes the recent progress in the effective field theory interpretation of charged lepton-flavour violating observables in conn…
Gluino Contribution to Radiative B Decays: Organization of QCD Corrections and Leading Order Results
在超对称框架下研究了具有一般味违反源的胶子对衰变b-> s γ的贡献。结果表明，当考虑QCD修正时，标准模型有效哈密顿量的相关算符基被扩大为包含：i）因子为α_s并由夸克质量m_b或m_c加权的磁算符和色磁算符; ii）低维的磁算符和色磁算符，也包含α_s; iii）因子为α_s ^[2]的四夸克算符。给出了数值结果，显示了首阶QCD修正对b-> s γ的包含分支比的影响。味违反超对称源的约束。
We build a highly predictive 3-3-1 model, where the field content is extended by including several $SU(3)_{L}$ scalar singlets and six right handed Majorana neutrinos. In our model the $SU(3)_{C}\times SU\left( 3\right) _{L}\times U\left( 1\right) _{X}$ gauge symmetry is supplemented by the $A_{4}\times Z_{4}\times Z_{6}\times Z_{16}\times Z_{16}^{\prime }$ discrete group, which allows to get a very good description of the low energy fermion flavor data. In the model under consideration, the $A_{4}\times Z_{4}\times Z_{6}\times Z_{16}\times Z_{16}^{\prime }$ discrete group is broken at very hi…
We present a detailed study of a combined singlet-doublet fermion and triplet scalar model for dark matter. These models have only been studied separately in the past. Together, they form a simple extension of the Standard Model that can account for dark matter and explain the existence of neutrino masses, which are generated radiatively. This holds even if singlet-doublet fermions and triplet scalars never contribute simultaneously to the dark matter abundance. However, this also implies the existence of lepton flavour violating processes. In addition, this particular model allows for gauge c…
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。
Since the discovery of neutrino oscillations many ideas have been put forward to explain the special features of the leptonic mixing and the differences with respect to the quark sector. In this talk I review some of these proposals, emphasizing especially their predictability. In the light of the new data, I first revisit fixed-point relations among mixing angles and phases. Then I briefly comment on radiative neutrino masses. Finally I discuss the role of flavour symmetries. Given the very many existing models I focus on two classes of models. On the one hand I illustrate the ability of mode…
We consider a two-Higgs-doublet extension of the Standard Model, with three right-handed neutrino singlets and the seesaw mechanism, wherein all the Yukawa-coupling matrices are lepton flavour-diagonal and lepton flavour violation is soft, originating solely in the non-flavour-diagonal Majorana mass matrix of the right-handed neutrinos. We consider the limit $m_R \to \infty$ of this model, where $m_R$ is the seesaw scale. We demonstrate that there is a region in parameter space where the branching ratios of all five charged-lepton decays $\ell_1^- \to \ell_2^- \ell_3^+ \ell_3^-$ are close to t…
An R-parity conserving radiative neutrino mass model without right-handed neutrinos
A. Zee（1986）和K.S. Babu（1988）是一个简单的辐射跷跷板模型，其中微小的中微子质量是在双圈水平上产生的。研究了R-宇称守恒下Zee-Babu模型的超对称推广.最轻的超伙伴粒子可以成为暗物质的候选者。我们发现，中微子的数据可以重现令人满意的当前数据从轻子味破坏，即使在的情况下，不是所有的超伙伴粒子是重的。在大型强子对撞机的现象学也进行了讨论。
