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在非零θ_{13}上得到结果后，μ-τ对称性有多好？

How good is μ-τsymmetry after results on non-zero θ_{13}?

Shivani Gupta, Anjan S. Joshipura, Ketan M. Patel

备注：
References added; Matches the version accepted for publication in JHEP
发表信息：
JHEP 09 (2013) 035
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摘要：

本文根据最近对非零反应堆混合角θ 13的观测，讨论了μ-τ交换对称性作为近似对称性（1）在味基中作用于中微子质量矩阵{ \cal M}_{νf}，（2）同时作用于带电轻子质量矩阵M_1和中微子质量矩阵M_v，（3）作用于拉格朗日量的可行性。在情形（1）中，μ-τ对称性破缺只有在反中微子谱或准边生中微子谱中才被认为是很小的（小于20-30%），而正常的谱系将大量破坏它。情况（2）的限制性更大，并且相对小的破缺要求只允许准边生谱。如果中微子的质量是从I型跷跷板机制获得的，那么在基本的拉格朗日量中μ-τ对称性的小破缺可能导致{ \cal M}_{νf}的大破缺，甚至中微子的分级谱也可能与拉格朗日量的μ-τ对称性的轻微破缺相一致。无中子双β衰变提供了区分上述情况的一个很好的方法。特别是，在未来的实验（如GERDA）中没有观察到信号将排除场景（1）和（2）。

英文摘要：

Viability of the μ-τinterchange symmetry imposed as an approximate symmetry (1) on the neutrino mass matrix {\cal M}_{νf} in the flavour basis (2) simultaneously on the charged lepton mass matrix M_l and the neutrino mass matrix M_νand (3) on the underlying Lagrangian is discussed in the light of recent observation of a non-zero reactor mixing angle θ_{13}. In case (1), μ-τsymmetry breaking may be regarded as small (less than 20-30%) only for the inverted or quasidegenerate neutrino mass spectrum and the normal hierarchy would violate it by a large amount. The case (2) is more restrictive and the requirement of relatively small breaking allows only the quasidegenerate spectrum. If neutrinos obtain their masses from the type-I seesaw mechanism then small breaking of the μ-τsymmetry in the underlying Lagrangian may result in a large breaking in {\cal M}_{νf} and even the hierarchical neutrino spectrum may also be consistent with mildly broken μ-τsymmetry of the Lagrangian. Neutrinoless double beta decay provides a good means of distinguishing above scenarios. In particular, non-observation of signal in future experiments such as GERDA would rule out scenarios (1) and (2).

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

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