Coutinho Antonio M, Crivellin Andreas, Manzari Claudio Andrea
Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland and Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
Phys Rev Lett. 2020 Aug 14;125(7):071802. doi: 10.1103/PhysRevLett.125.071802.
Recently, discrepancies of up to 4σ between the different determinations of the Cabibbo angle were observed. In this context, we point out that this "Cabibbo-angle anomaly" can be explained by lepton flavor universality violating new physics in the neutrino sector. However, modified neutrino couplings to standard model gauge bosons also affect many other observables sensitive to lepton flavor universality violation, which have to be taken into account in order to assess the viability of this explanation. Therefore, we perform a model-independent global analysis in a Bayesian approach and find that the tension in the Cabibbo angle is significantly reduced, while the agreement with other data is also mostly improved. In fact, nonzero modifications of electron and muon neutrino couplings are preferred at more than 99.99% C.L. (corresponding to more than 4σ). Still, since constructive effects in the muon sector are necessary, simple models with right-handed neutrinos (whose global fit we update as a by-product) cannot fully explain data, pointing towards more sophisticated new physics models.
最近，人们观察到不同方法测定的卡比博角之间存在高达4σ的差异。在此背景下，我们指出，这种“卡比博角反常”可以由中微子领域违反轻子味普适性的新物理来解释。然而，修改后的中微子与标准模型规范玻色子的耦合也会影响许多其他对轻子味普适性违反敏感的可观测量，为了评估这种解释的可行性，必须将这些因素考虑在内。因此，我们采用贝叶斯方法进行了一次与模型无关的全局分析，发现卡比博角的张力显著降低，同时与其他数据的一致性也大多得到改善。事实上，电子和μ子中微子耦合的非零修正以超过99.99%的置信水平（对应于超过4σ）更为可取。不过，由于μ子领域需要有建设性的效应，带有右手中微子的简单模型（我们顺便更新了其全局拟合）无法完全解释数据，这指向了更复杂的新物理模型。
