论文标题
Beta衰减是对Lepton风味普遍性的敏感探针
Beta decays as sensitive probes of lepton flavor universality
论文作者
论文摘要
核$β$衰减以及中子的衰减是超出标准模型（SM）以外的物理学良好的低能探针。特别是，通过根据晶格QCD确定的核子$ g_a $的轴向矢量耦合，实验和SM预测之间的比较通常用于在右手电流上得出约束。此外，除了从$β$衰减中的Kaon衰减中的CKM元素$ V_ {US} $外，$ v_ {ud} $是测试CKM Unitarity的关键输入。在这里，我们指出，有关$β$衰减的可用信息可以重新解释为对Lepton风味普遍性（LFU）的严格测试。实际上，我们发现，$ v_ {us} $的比率超过$β$衰减的$ v_ {us} $（假设CKM Unitarity）在$ W $ -W $ -UM-$ $ -UM-$ n $ cuplings中对LFU违规（LFU）非常敏感。 $（v_ {ud}/v_ {us}）^2 \ sim 20 $。从这个角度来看，违反CKM Unitarity的最新提示可以看作是LFUV的进一步证据，适合Semi-Leptonic $ b $衰减所展示的现有图片，以及Muon和Electron的异常磁矩。最后，我们对可观察到的LFU可以达到的未来敏感性发表评论，并讨论LFU的互补探针，该探针可能达到相似的精度，例如$γ（π\toμν）/γ（π\ to e em ev \ e e ev to e e ev to e e ev to e e em e e e e fcc，
Nuclear $β$ decays as well as the decay of the neutron are well-established low-energy probes of physics beyond the Standard Model (SM). In particular, with the axial-vector coupling of the nucleon $g_A$ determined from lattice QCD, the comparison between experiment and SM prediction is commonly used to derive constraints on right-handed currents. Further, in addition to the CKM element $V_{us}$ from kaon decays, $V_{ud}$ from $β$ decays is a critical input for the test of CKM unitarity. Here, we point out that the available information on $β$ decays can be re-interpreted as a stringent test of lepton flavor universality (LFU). In fact, we find that the ratio of $V_{us}$ from kaon decays over $V_{us}$ from $β$ decays (assuming CKM unitarity) is extremely sensitive to LFU violation (LFUV) in $W$-$μ$-$ν$ couplings thanks to a CKM enhancement by $(V_{ud}/V_{us})^2\sim 20$. From this perspective, recent hints for the violation of CKM unitarity can be viewed as further evidence for LFUV, fitting into the existing picture exhibited by semi-leptonic $B$ decays and the anomalous magnetic moments of muon and electron. Finally, we comment on the future sensitivity that can be reached with this LFU violating observable and discuss complementary probes of LFU that may reach a similar level of precision, such as $Γ(π\toμν)/Γ(π\to eν)$ at the PEN and PiENu experiments or even direct measurements of $W\toμν$ at an FCC-ee.
