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Unitarity in Higher Dimensions and Gauge Unification

R. Sekhar Chivukula·Duane A. Dicus·Hong-Jian He·S. Nandi
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Abstract

Unitarity of the 4d standard model is ensured by the conventional Higgs mechanism with a fundamental spin-0 Higgs boson, responsible for gauge boson mass-generations. On the contrary Kaluza-Klein (KK) compactification of extra spatial dimensions can geometrically realize the gauge boson mass generation without invoking a fundamental Higgs scalar. We reveal that massive gauge boson scattering in the compactified theories is unitary at low energies, and the unitarity violation is {\it delayed} to the intrinsic ultraviolet (UV) scale of the higher dimensional gauge theory. We demonstrate that this is a generic consequence of the ``geometric Higgs mechanism'' (GHM), manifested via Kaluza-Klein equivalence theorem (KK-ET). We further show that the presence of many gauge KK states below the UV cutoff scale imposes strong bounds on the highest KK level (N_KK). Applying these bounds to higher-dimensional SUSY GUTs implies that only a small number of KK states can be used to accelerate gauge coupling unification, and suggests that the GUT scale in the 5d minimal SUSY SU(5) is above 10^{14} GeV.

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R. Sekhar Chivukula, Duane A. Dicus, Hong-Jian He, S. Nandi. 2004-02-21. Unitarity in Higher Dimensions and Gauge Unification. https://arxiv.org/abs/hep-ph/0402222

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