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UED的Kaluza-Klein数破坏机制及其对LHC的启示

A Mechanism for Kaluza-Klein Number Violation in UED and Implications for LHC

C. D. McMullen, S. Nandi

备注：
22 pages, 5 figures; uploaded as a PDF file, thus it will not be available as a PostScript file; version 2 includes a discussion of bounds from the T-parameter, including ways that these bounds may be relaxed, and extension of the range of some figures to 2.4 TeV
发表信息：
J.Phys.G35:095002,2008
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摘要：

如果希格斯粒子没有传播到另一个普遍的额外维度，那么树级卡鲁扎-克莱因数在汤川相互作用中是不守恒的。这导致了零模费米子和它们相关的卡鲁扎-克莱因激发之间的混合。对于顶夸克来说，这种效应可能相当大，因为它的质量（171.4 ± 2.1 GeV）大约是目前具有一个普遍额外维度的夸克的卡鲁扎-克莱因激发的Tevatron质量束缚（大约350-400 GeV）的一半。与SM相反，对角化质量矩阵的双酉变换由于5D动力学项的存在而不对角化有效的4D Yukawa耦合矩阵。由于5D理论的一个独特的特征，这导致在规范扇区中违反了树级卡鲁扎-克莱因数守恒。这使得费米子的卡鲁扎-克莱因激发可以单独产生，并在规范扇区中开辟了新的衰变通道。计算了在大型强子对撞机上非普适Higgs模型中顶夸克和底夸克最低激发态的产生截面，并考虑了它们随后的衰变.影响相当大：例如，底夸克的卡鲁扎-克莱因激发的对产生将导致一对顶夸克加上一对带电的弱规范玻色子。由于产生是通过强相互作用，这样的最终状态脱颖而出，以及对标准模型的背景下，并在大型强子对撞机的大范围的紧凑化尺度观察。最后，我们讨论了这样一个模型的T-参数的影响，并提出了一个模型的最大混合的紧化规模可能是一个普遍的额外的尺寸一样大。

英文摘要：

If the Higgs does not propagate into an otherwise universal extra dimension, then tree-level Kaluza-Klein number is not conserved in the Yukawa interactions. This leads to mixing between zero-mode fermions and their associated Kaluza-Klein excitations. The effect can be quite large for the top quark, since its mass (171.4 plus or minus 2.1 GeV) is approximately one-half the current Tevatron mass bound (about 350-400 GeV) for Kaluza-Klein excitations of quarks with one universal extra dimension. In contrast to the SM, the bi-unitary transformation that diagonalizes the mass matrix does not diagonalize the effective 4D Yukawa coupling matrix because of the presence of the 5D kinetic terms. This leads to violation of tree-level Kaluza-Klein number conservation in the gauge sector due to a unique feature of the 5D theory. This allows Kaluza-Klein excitations of the fermions to be produced singly, and opens up new decay channels in the gauge sector. We compute the cross section for the production of the lowest-lying Kaluza-Klein excitations of the top and bottom quarks in the non-universal Higgs model at the Large Hadron Collider, and consider their subsequent decays. The effect is quite large: For example, pair production of Kaluza-Klein excitations of the bottom quark will lead to a pair of top quarks plus a pair of charged weak gauge bosons. Since the production is via the strong interaction, such final states stand out well against the Standard Model background, and are observable at the LHC for a wide range of compactification scales. Finally, we discuss the effects that such a model has on the T- parameter, and propose a model with maximal mixing where the compactification scale may be as large as a universal extra dimension.

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