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arXiv 1406.0102hep-phhep-ex
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Down-Quark汤川联轴器的间接处理

An Indirect Handle on the Down-Quark Yukawa Coupling

Florian Goertz

摘要:

要测量上夸克和下夸克的汤川耦合,Y_{u,d},似乎远远超出了粒子物理学目前和(不久的)未来实验的能力。通过对夸克质量和汤川耦合之间的潜在不对准进行一般性分析,我们得到了对诱导的变味中性流(FCNC)的大小的预测,这取决于第一代夸克的物理汤川耦合的转变。我们发现下夸克Yukawa Y_d的-100%位移一般会导致与K介子物理相冲突的ds跃迁。这已经可以被视为下夸克与新发现的希格斯玻色子之间存在非零直接耦合的证据。因此,对某些已经受到很好约束的过程的不观察就变成了对有效标准模型的物理参数的一种有力的间接测量,到目前为止,这些物理参数基本上不受实验的约束,而且用其他方法获得这些物理参数极具挑战性。特别是,我们已经可以推断出,Y_d应该从其标准模型值变化最多~50%,除非新的物理效应与SM汤川耦合对齐。然而,这样的(正交)排列方案通常更容易在LHC上进行测试。类似地,上夸克扇区中FCNC限制的改进可以导致关于上夸克的物理汤川耦合的有价值的信息。

英文摘要:

To measure the Yukawa couplings of the up and down quarks, Y_{u,d}, seems to be far beyond the capabilities of current and (near) future experiments in particle physics. By performing a general analysis of the potential misalignment between quark masses and Yukawa couplings, we derive predictions for the magnitude of induced flavor-changing neutral currents (FCNCs), depending on the shift in the physical Yukawa coupling of first-generation quarks. We find that a shift of -100% in the down-quark Yukawa Y_d would generically result in ds transitions in conflict with Kaon physics. This could already be seen as evidence for a non-vanishing direct coupling of the down quark to the newly discovered Higgs boson. The non-observation of certain, already well-constrained, processes is thus turned into a powerful indirect measure of physical parameters of the effective Standard-Model, which are so far basically unconstrained from experiment and extremely challenging to access with other methods. In particular, we can already deduce that Y_d should vary at most by ~50% from its Standard Model value, barring an alignment of new physics effects with the SM Yukawa couplings. Such an (orthogonal) alignment scenario is however in general much easier to test at the LHC. Similarly, improvements in limits on FCNCs in the up-type quark sector can lead to valuable information on the physical Yukawa coupling of the up-quark.

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