标题： CKM 单位性问题：TeV 尺度上新物理的蛛丝马迹？ 显示英文标题

标题： The CKM unitarity problem: A trace of new physics at the TeV scale?

摘要： 在最近对$V_{us}$和$V_{ud}$的高精度测定之后，CKM 矩阵的第一行显示出超过$4\sigma$的偏离单位性。 为了填补这一空白，可以研究超出标准模型的两种可能情景。 如果第四个夸克$b'$参与混合，且$\vert V_{ub'} \vert \sim0.04$成立，那么它的质量应不超过约 6 TeV。 另一种解决方案可以通过引入作用于轻子族之间并在约 6 TeV 尺度自发破缺的规范水平族对称性来实现。 由于该对称性的规范玻色子以与标准模型正干涉的方式参与μ子衰变，因此费米常数略小于μ子衰变常数，从而恢复了单位性。 此外，在这些 CKM 矩阵元确定的背景下，讨论了中子寿命问题，即束流和陷阱实验测得的中子寿命存在约$4\sigma$的差异。 显示英文摘要

摘要： After the recent high precision determinations of $V_{us}$ and $V_{ud}$, the first row of the CKM matrix shows more than $4\sigma$ deviation from unitarity. Two possible scenarios beyond the Standard Model can be investigated in order to fill the gap. If a 4th quark $b'$ participates in the mixing, with $\vert V_{ub'} \vert \sim0.04$, then its mass should be no more than 6 TeV or so. A different solution can come from the introduction of the gauge horizontal family symmetry acting between the lepton families and spontaneously broken at the scale of about 6 TeV. Since the gauge bosons of this symmetry contribute to muon decay in positive interference with Standard Model, the Fermi constant is slightly smaller than the muon decay constant so that unitarity is recovered. Also the neutron lifetime problem, that is about $4\sigma$ discrepancy between the neutron lifetimes measured in beam and trap experiments, is discussed in the light of the these determinations of the CKM matrix elements.