We analyze the effect of flat universal extra dimensions (i.e., extra dimensions accessible to all SM fields) on the process b --> s gamma. With one Higgs doublet, the dominant contribution at one-loop is from Kaluza-Klein (KK) states of the charged would-be-Goldstone boson (WGB) and of the top quark. The resulting constraint on the size of the extra dimension is comparable to the constraint from T parameter. In two-Higgs-doublet model II, the contribution of zero-mode and KK states of physical charged Higgs can cancel the contribution from WGB KK states. Therefore, in this model, there is no constraint on the size of the extra dimensions from the process b --> s gamma and also the constraint on the mass of the charged Higgs from this process is weakened compared to 4D. In two-Higgs-doublet model I, the contribution of the zero-mode and KK states of physical charged Higgs and that of the KK states of WGB are of the same sign. Thus, in this model and for small tan beta, the constraint on the size of the extra dimensions is stronger than in one-Higgs-doublet model and also the constraint on the mass of the charged Higgs is stronger than in 4D. (C) 2001 Published by Elsevier Science B.V. References: 16
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机译：我们分析了平坦的通用额外维度（即所有 SM 场都可以访问的额外维度）对过程 b --> s gamma 的影响。对于一个希格斯双峰，单环的主要贡献来自带电的戈德斯通玻色子（WGB）和顶夸克的Kaluza-Klein（KK）态。对额外维度大小的约束结果与 T 参数的约束相当。在双希格斯双峰模型II中，物理带电希格斯的零模态和KK态的贡献可以抵消WGB KK态的贡献。因此，在这个模型中，对过程 b --> s gamma 的额外维度的大小没有约束，并且与 4D 相比，该过程对带电希格斯质量的约束也减弱了。在双希格斯双峰模型I中，物理带电希格斯的零模态和KK态与WGB的KK态的贡献是相同的符号。因此，在这个模型中，对于小的tan beta，对额外维度大小的约束比单希格斯双重态模型更强，而且对带电希格斯质量的约束也比4D更强。 （C） 2001年由Elsevier Science B.V.出版 [参考文献： 16]
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