arXiv 1704.005102017-04-03hep-lat

从$K$得到的$|V_{us}|$理论上衰变

$|V_{us}|$ from $K$ decays in theory

S. Simula

备注：: Invited talk delivered at the 9th International Workshop on the CKM Unitarity Triangle, 28 November - 3 December 2016, Tata Institute for Fundamental Research (TIFR), Mumbai (India)

摘要：

轻子和半轻子K介子衰变代表了迄今为止从实验中提取Cabibbo角的黄金模式，前提是相关的强子量，即K介子和π轻子衰变常数之比$f_K / f_π$，以及零四动量转移时的半轻子矢量形状因子$f_+(0)$，可以从QCD精确计算。在过去的几年里，使用大规模的格子QCD模拟，$f_K / f_π$和$f_+(0)$的确定已经达到了令人印象深刻的精度水平（$\approx 0.3 \%$），这是预计将在不久的将来进一步提高。然而，在精确到千分之一的水平上，电磁和强同位旋破缺效应都不能再被忽略了。本文简要地介绍了一种新的确定带电赝标介子轻子衰变速率中QCD+QED效应的晶格策略，并给出了在$π_{\ell 2}$和$K_{\ell 2}$衰变情况下的初步结果。对于半轻子$K_{\ell 3}$衰变，指出在实验所涵盖的整个运动学范围内确定相关的形状因子对于更严格地检验标准模型是必要的。在这方面，基于欧洲扭曲质量协作（ETMC）的唯一现有结果的观点是相当令人鼓舞的。

英文摘要：

Leptonic and semileptonic kaon decays represent till now the golden modes for the extraction of the Cabibbo angle from experiments, provided the relevant hadronic quantities, namely the ratio of the kaon and pion leptonic decay constants, $f_K / f_π$, and the semileptonic vector form factor at zero four-momentum transfer, $f_+(0)$, are computed accurately from QCD. In the last years, using large-scale lattice QCD simulations, the determination of both $f_K / f_π$ and $f_+(0)$ has reached an impressive level of precision ($\approx 0.3 \%$), which is expected to be further improved in the near future. However, at a permille level of precision both electromagnetic and strong isospin-breaking effects cannot be neglected anymore. In this contribution a new lattice strategy aiming at determining QCD+QED effects in the inclusive leptonic decay rates of charged pseudoscalar mesons is briefly illustrated, and the preliminary results obtained in the case of $π_{\ell 2}$ and $K_{\ell 2}$ decays are presented. As for the semileptonic $K_{\ell 3}$ decays, it is pointed out that the determination of the relevant form factors in the full kinematical range covered by the experiments is necessary for a more stringent test of the Standard Model. In this respect the perspectives based on the only existing results from the European Twisted Mass Collaboration (ETMC) are quite encouraging.

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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英文摘要：

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