arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2103.05549hep-phhep-exnucl-exnucl-th
收藏

CKM反常是由类矢量夸克引起的吗?风味变化和标准模型精密度试验的限值

Are the CKM anomalies induced by vector-like quarks? Limits from flavor changing and Standard Model precision tests

Benedetta Belfatto, Zurab Berezhiani

摘要:

最近对$V_{us}$和$V_{ud}$的高精度测定表明CKM矩阵的第一行中存在异常。也就是说,从超允许β衰变中确定$V_{ud}$和从K介子衰变中确定$V_{us}$意味着在大约$4σ$水平上违反了第一行么正性。此外,在从轻子$K\mu2$和半轻子$K\ell3$ K介子衰变中得到的$V_{us}$的测定之间存在着张力。这些差异可以解释,如果存在额外的矢量类夸克在TeV尺度,有足够大的混合轻夸克。特别是,额外的矢量状弱单线态夸克可以被认为是CKM么正性问题的解决方案,而额外的矢量状弱双线态原则上可以解决所有的张力。这种混合的影响进行检查对风味变化的现象和SM精度测试。我们分别考虑额外的下型等单线态,上型等单线态和包含额外的上型和下型夸克的等重线的影响,并确定每种情况下可用的参数空间。我们发现,味道变化现象的实验约束变得更加严格,更大的群众,使额外的物种应该有质量不超过几个TeV。此外,只有一种类型的额外多重态不能完全解释所有的差异,需要它们的组合。我们表明,这些方案是可测试的未来的实验。也就是说,如果额外的类矢量夸克是造成CKM异常的原因,那么在几TeV的尺度上至少应该发现其中之一,并且如果$2$的实验精度提高$Z$的1倍左右,那么轻夸克与$Z$ -玻色子耦合的异常弱同位旋破坏应该被探测到。

英文摘要:

Recent high precision determinations of $V_{us}$ and $V_{ud}$ indicate towards anomalies in the first row of the CKM matrix. Namely, determination of $V_{ud}$ from superallowed beta decays and of $V_{us}$ from kaon decays imply a violation of first row unitarity at about $4σ$ level. Moreover, there is tension between determinations of $V_{us}$ obtained from leptonic $K\mu2$ and semileptonic $K\ell3$ kaon decays. These discrepancies can be explained if there exist extra vector-like quarks at the TeV scale, which have large enough mixings with the lighter quarks. In particular, extra vector-like weak singlets quarks can be thought as a solution to the CKM unitarity problem and an extra vector-like weak doublet can in principle resolve all tensions. The implications of this kind of mixings are examined against the flavour changing phenomena and SM precision tests. We consider separately the effects of an extra down-type isosinglet, up-type isosinglet and an isodoublet containing extra quarks of both up and down type, and determine available parameter spaces for each case. We find that the experimental constraints on flavor changing phenomena become more stringent with larger masses, so that the extra species should have masses no more than few TeV. Moreover, only one type of extra multiplet cannot entirely explain all the discrepancies, and some their combination is required. We show that these scenarios are testable with future experiments. Namely, if extra vector-like quarks are responsible for CKM anomalies, then at least one of them should be found at scale of few TeV, and anomalous weak isospin violating $Z$-boson couplings with light quarks should be detected if the experimental precision on $Z$ hadronic decay rate is improved by a factor of $2$ or so.

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。

↑