The rare flavor-changing top quark decay $t\to cZ$ is a clear sign of new physics and experimentally very interesting due to the huge number of top quarks produced at the LHC. However, there are few (viable) models which can generate a sizable branching ratio for $t\to cZ$—in fact vectorlike quarks seem to be the only realistic option. In this paper, we investigate all three representations (under the Standard Model gauge group) of vectorlike quarks ($U$, $Q_1$ and $Q_7$) that can generate a sizable branching ratio for $t\to cZ$ without violating bounds from $B$ physics. Importantly, these are exactly the three vectorlike quarks which can lead to a sizable positive shift in the prediction for $W$ mass, via the couplings to the top quark also needed for a sizable $\mathrm{Br}(t\to cZ)$. Calculating and using the one-loop matching of vectorlike quarks on the Standard Model effective field theory, we find that $\mathrm{Br}(t\to cZ)$ can be of the order of ${10}^{-6}$, ${10}^{-5}$ and ${10}^{-4}$ for $U$, $Q_1$ and $Q_7$, respectively, and that in all three cases the large $W$ mass measurement can be accommodated.

中文翻译：

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Larget→cZ 是 Wmass 中类矢量夸克的标志

罕见的改变味道的顶夸克衰变$吨\to CZ$由于大型强子对撞机产生了大量的顶夸克，这是新物理学的明显标志，并且在实验上非常有趣。然而，很少有（可行的）模型可以为$吨\to CZ$——事实上，类矢量夸克似乎是唯一现实的选择。在本文中，我们研究了类矢量夸克的所有三种表示（在标准模型规范组下）（$ü$,${问}_1$和${问}_7$) 可以产生相当大的支化率$吨\to CZ$在不违反界限的情况下$乙$物理。重要的是，这些正是三个矢量夸克，它们可以导致对$W$质量，通过耦合到顶夸克也需要相当大的$溴(吨\to CZ)$. 在标准模型有效场论上计算并使用类矢量夸克的单环匹配，我们发现$溴(吨\to CZ)$可以是${10}^{-6}$,${10}^{-5}$和${10}^{-4}$为了$ü$,${问}_1$和${问}_7$，并且在所有三种情况下，大$W$可以进行质量测量。