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arXiv 1408.3191hep-ph
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II型跷跷板对$μ-τ$对称性、轻子生成和轻子味破坏的微扰

Perturbations to $μ-τ$ Symmetry, Leptogenesis and Lepton Flavour Violation with Type II Seesaw

Manikanta Borah, Debasish Borah, Mrinal Kumar Das, Sudhanwa Patra

备注：
v2: Added references, to appear in Phys. Rev. D. arXiv admin note: text overlap with arXiv:1403.7636, arXiv:1303.1758
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摘要：

研究了通过微扰$μ-τ$对称中微子质量矩阵产生非零反应堆混合角$θ_{13}$的可能性。第一阶$μ-τ$对称中微子质量矩阵来自I型跷跷板机制，而对$μ-τ$对称性的扰动来自II型跷跷板项。我们考虑了四种不同的$μ-τ$对称性：双峰混合（BM）、三双峰混合（TBM）、半球混合（HM）和黄金比例混合（GRM），它们都产生了$θ_{13} = 0, θ_{23} = \fracπ{4}$，但太阳混合角$θ_{12}$的非零值不同。我们假设一个最小的$μ-τ$对称破缺的第二类跷跷板质量矩阵作为微扰，并计算了中微子振荡参数作为第二类跷跷板强度的函数。然后，我们考虑的起源非平凡轻子CP阶段的带电轻子部门和计算轻子不对称性所产生的最轻的右手中微子衰变，将存在的I型和II型跷跷板。我们约束II型跷跷板强度以及轻子CP相位（因此带电轻子扇区）通过比较我们的结果与实验中微子振荡参数以及普朗克束缚的重子光子比。最后，我们扩展了我们的分析轻子味违反衰变，如$μ\to e γ$和$μ\to eee$由于交换TeV尺度的希格斯三重态标量在低尺度II型跷跷板框架。这些轻子味过程的分支比检查与小II型扰动项$ω$和估计值是非常接近的实验界来自目前的搜索实验。

英文摘要：

We study the possibility of generating non-zero reactor mixing angle $θ_{13}$ by perturbing the $μ-τ$ symmetric neutrino mass matrix. The leading order $μ-τ$ symmetric neutrino mass matrix originates from type I seesaw mechanism whereas the perturbations to $μ-τ$ symmetry originate from type II seesaw term. We consider four different realizations of $μ-τ$ symmetry: Bimaximal Mixing(BM), Tri-bimaximal Mixing (TBM), Hexagonal Mixing (HM) and Golden Ratio Mixing (GRM) all giving rise to $θ_{13} = 0, θ_{23} = \fracπ{4}$ but different non-zero values of solar mixing angle $θ_{12}$. We assume a minimal $μ-τ$ symmetry breaking type II seesaw mass matrix as a perturbation and calculate the neutrino oscillation parameters as a function of type II seesaw strength. We then consider the origin of non-trivial leptonic CP phase in the charged lepton sector and calculate the lepton asymmetry arising from the lightest right handed neutrino decay by incorporating the presence of both type I and type II seesaw. We constrain the type II seesaw strength as well as leptonic CP phase (and hence the charged lepton sector) by comparing our results with experimental neutrino oscillation parameters as well as Planck bound on baryon to photon ratio. Finally, we extend our analysis on lepton flavour violating decays like $μ\to e γ$ and $μ\to eee$ due to exchange of TeV scale Higgs triplet scalar within the low scale type II seesaw framework. The branching ratios for these lepton flavour processes are examined with the small type II perturbation term $ω$ and the estimated values are very close to the experimental bound coming from current search experiments.

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