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Contributions to $$ZZV^*$$ Z Z V ∗ ( $$V=\gamma ,Z,Z'$$ V = γ , Z , Z ′ ) couplings from CP violating flavor changing couplings
The European Physical Journal C ( IF 4.2 ) Pub Date : 2021-04-10 , DOI: 10.1140/epjc/s10052-021-09093-w
A. I. Hernández-Juárez , A. Moyotl , G. Tavares-Velasco

The one-loop contributions to the trilinear neutral gauge boson couplings \(ZZV^*\) (\(V=\gamma ,Z,Z'\)), parametrized in terms of one CP-conserving \(f_5^{V}\) and one CP-violating \(f_4^{V}\) form factors, are calculated in models with CP-violating flavor changing neutral current couplings mediated by the Z gauge boson and an extra neutral gauge boson \(Z'\). Analytical results are presented in terms of Passarino-Veltman scalar functions. Constraints on the vector and axial couplings of the Z gauge boson \(\left| g_{{VZ}}^{tu}\right| < 0.0096\) and \(\left| g_{{VZ}}^{tc}\right| <0.011\) are obtained from the current experimental data on the \(t\rightarrow Z q\) decays. It is found that in the case of the \(ZZ\gamma ^*\) vertex the only non-vanishing form factor is \(f_5^{\gamma }\), which can be of the order of \(10^{-3}\), whereas for the \(ZZZ^*\) vertex both form factors \(f_5^{Z}\) and \(f_4^{Z}\) are non-vanishing and can be of the order of \(10^{-6}\) and \(10^{-5}\), respectively. Our estimates for \(f_5^{\gamma }\) and \(f_5^{Z}\) are smaller than those predicted by the standard model, where \(f_4^{Z}\) is absent up to the one loop level. We also estimate the \(ZZ{Z'}^{*}\) form factors arising from both diagonal and non-diagonal \(Z'\) couplings within a few extension models. It is found that in the diagonal case \(f_{5}^{Z'}\) is the only non-vanishing form factor and its real and imaginary parts can be of the order of \(10^{-1}\)\(10^{-2}\) and \( 10^{-2}\)\(10^{-3}\), respectively, with the dominant contributions arising from the light quarks and leptons. In the non-diagonal case \(f_{5}^{Z^\prime }\) can be of the order of \(10^{-4}\), whereas \(f_4^{Z'}\) can reach values as large as \(10^{-7}\)\(10^{-8}\), with the largest contributions arising from the \(Z'tq\) couplings.

A preprint version of the article is available at ArXiv.


中文翻译:

CP违反风味改变耦合对$$ ZZV ^ * $$ ZZV ∗($$ V = \ gamma,Z,Z'$$ V =γ,Z,Z')耦合的贡献

对三线性中性规范玻色子耦合\(ZZV ^ * \)\(V = \ gamma,Z,Z'\))的单环贡献是根据一个CP守恒\(f_5 ^ {V} \)和一个CP -violating \(F_4 ^ {V} \)的形状因子,在模型计算与CP -violating风味改变由介导的中性电流联轴器ž规范玻色子和一个额外的中性规范玻色子\(Z'\)。分析结果以Passarino-Veltman标量函数表示。Z规格玻色子\(\ left | g _ {{VZ}} ^ {tu} \ right | <0.0096 \)的矢量和轴向耦合的约束,\(\ left | g _ {{VZ}} ^ {tc} \ right | <0.011 \)是从\(t \ rightarrow Z q \)衰减的当前实验数据获得的。发现在\(ZZ \ gamma ^ * \)顶点的情况下,唯一不消失的形状因子是\(f_5 ^ {\ gamma} \),其大小可能约为\(10 ^ { -3} \),而对于\(ZZZ ^ * \)顶点,形状因数\(f_5 ^ {Z} \)\(f_4 ^ {Z} \)都不会消失,并且可以为\(10 ^ {-6} \)\(10 ^ {-5} \)。我们对\(f_5 ^ {\ gamma} \)\(f_5 ^ {Z} \)的估计小于标准模型所预测的值,在标准模型中,直到一个循环级别都没有\(f_4 ^ {Z} \)。我们还估计了一些扩展模型中对角和非对角\(Z'\)耦合产生的\(ZZ {Z'} ^ {*} \)形状因数。发现在对角线情况下\(f_ {5} ^ {Z'} \)是唯一不消失的形状因数,其实部和虚部可以为\(10 ^ {-1} \ )\(10 ^ {-2} \)\(10 ^ {-2} \)\(10 ^ {-3} \),分别由轻夸克和轻子产生。在非对角情况下,\(f_ {5} ^ {Z ^ \ prime} \)的数量级为\(10 ^ {-4} \),而\(f_4 ^ {Z'} \)可以达到\(10 ^ {-7} \)\(10 ^ {-8} \)大的值\(Z'tq \)耦合产生的最大贡献。

该文章的预印本可在ArXiv上获得。
更新日期:2021-04-11
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