The determination of $α_s$ from hadronic $τ$ decays is revisited, with a special emphasis on the question of higher-order perturbative corrections and different possibilities of resumming the perturbative series with the renormalisation group: fixed-order (FOPT) vs. contour-improved perturbation theory (CIPT). The difference between these approaches has evolved into a systematic effect that does not go away as higher orders in the perturbative expansion are added. We attempt to clarify under which circumstances one or the other approach provides a better approximation to the true result. To this end, we propose to describe the Adler function series by a model that includes the exactly known coefficients and theoretical constraints on the large-order behaviour originating from the operator product expansion and the renormalisation group. Within this framework we find that while CIPT is unable to account for the fully resummed series, FOPT smoothly approaches the Borel sum, before the expected divergent behaviour sets in at even higher orders. Employing FOPT up to the fifth order to determine $α_s$ in the $\MSb$ scheme, we obtain $α_s(M_τ)=0.320 {}^{+0.012}_{-0.007}$, corresponding to $α_s(M_Z) = 0.1185 {}^{+0.0014}_{-0.0009}$. Improving this result by including yet higher orders from our model yields $α_s(M_τ)=0.316 \pm 0.006$, which after evolution leads to $α_s(M_Z) = 0.1180 \pm 0.0008$. Our results are lower than previous values obtained from $τ$ decays.
In the framework of precision experiments, the search for electric dipole moments and the precise determination of magnetic dipole moments (g-2) have since long been of prime interest. Hadronic decays offer the best accuracy, since only the kinematic information carried by a single neutrino per decay is lost. Thus, they reveal more easily precious information on the helicity of the initial tau lepton. However, in contrast to one- or two-body hadronic final states, the description of hadronic multi-body final states depends on the model for the hadronic current. In this work, we determine how t…
Within the Standard Model Effective Field Theory framework, with operators up to dimension 6, we perform a model-independent analysis of the lepton-flavour-violating processes involving tau leptons. Namely, we study hadronic tau decays and $\ell$--$τ$ conversion in nuclei, with $\ell = e,μ$. Based on available experimental limits, we establish constraints on the Wilson coefficients of the operators contributing to these processes. Our work paves the way to extract the related information from Belle II and foreseen future experiments.
Within the Standard Model Effective Field Theory framework, with operators up to dimension 6, we perform a model-independent analysis of the lepton-flavour-violating processes involving tau leptons. Namely, we study hadronic tau decays and $\ell$-$τ$ conversion in nuclei ($\ell=e,μ$). Based on available experimental limits, we establish constraints on the Wilson coefficients of the operators contributing to these processes. The related information from Belle II and foreseen future experiments can be easily incorporated into the resulting framework.
本博士论文利用包含共振场的手征拉格朗日量研究了τ轻子的一些强子和辐射衰变。在理论介绍之后，分析了$(πππ)^-$、$(KKπ)^-$、$η^{(\prime)} π^- π^0$强子态和$τ\to (π/K)^- γν_tau$的衰变.对3 π介子模的结构函数分析，三介子模中微分衰变宽度与两粒子不变质量的关系，以及对$τ\to$ η^{（\prime）} π^- π^0 ν_τ $ processes within a single-angle mixing scheme for the $ η $ and $ η^ \prime $介子的简化研究，也作了讨论。
Exclusive hadronic Tau decays in the resonance effective action of QCD
到目前为止，强子弱流的矢量和轴矢量分量的形状因子的研究已经进行了大量的基础强相互作用的模型化。虽然了解所涉及的动力学非常重要，但实验数据的数量和质量开始显示出与分析模型的一些差异。此外，从理论的角度来看，这些模型中的大多数与量子色动力学（QCD）不一致。我们提出了一个基于QCD的模型无关的程序来分析这些衰变，通过使用共振手征理论，低能量有效作用的QCD在相关的共振区。在这个框架下，我们研究了Tau（-）-> Pi（-）Pi（0）nu_tau中Rho介子的强子离壳层宽度和π介子的矢量形状因子.我们还讨论了Tau（-）->（Pi Pi Pi）（-）nu_tau衰变.
我们考虑了τ-> 3 pi nu_ tau和4 pi nu_ tau（Δ S = 0）以及τ-> K pi pi nu_tau（Δ S = 1）中的CP破坏效应，假设这些过程的通常标准模型振幅干扰了带电希格斯玻色子介导的类似振幅。在Delta S = 0的情况下，我们特别关注中间共振过程tau -> V pi nu_tau（V=omega，rho和a_1），并考虑三个CP-奇数观测值-部分速率不对称性，偏振相关不对称性和三重产物不对称性。在Delta S = 1的情况下，我们研究部分利率不对称，两个“修改”利率不对称，和三重产品不对称。预计Delta S = 0和Delta S = 1情况下的部分速率不对称性较小。对其他不对称性的评估表明，它们可能是可以测量的。
The form factors for hadronic tau decay using background field method
在两体强子τ衰变过程中，如τ → K π（eta）nu，矢量介子起着重要的作用。Belle和Babar测量了τ-> K π nu衰变的强子不变质谱。为了将谱与理论预测进行比较，我们在Kimura：2012 nx中开发了具有矢量介子的手征拉格朗日量。我们计算了强子τ衰变的形状因子，并考虑了Nambu Goldstone玻色子的量子修正。我们还展示了如何用背景场方法对任意圈数的Feynman图的发散进行重正化，以及如何确定一圈内的反项，在本报告中，我们讨论了Kimura：2012 nx在考虑单圈Feynman图的情况下的重正化。
我们研究了Delta S=0衰变tau -> omega pi nu_tau和tau -> a_1 pi nu_tau以及Delta S=1衰变tau -> K pi pi nu_tau中的CP破坏。我们假设新的物理是带电的希格斯粒子。我们发现，相当大的CP违反的影响是可能的，在tau -> a_1 π nu_tau（偏振相关的速率不对称性）和tau -> omega π nu_ tau（三重产品不对称性）。Δ S=1衰减τ-> K pi pi nu_tau可以通过几个共振进行。我们构建了两个修改后的速率不对称性和三重产品不对称性，这种衰变，并讨论这些不对称性的潜在敏感性。
