Novel universality and Higgs decay H -> \gamma \gamma, gg in the SO(5) x U(1) gauge-Higgs unification

Abstract

The SO(5) x U(1) gauge-Higgs unification in the Randall-Sundrum warped space with the Higgs boson mass m_H=126 GeV is constructed. An universal relation is found between the Kaluza-Klein (KK) mass scale $m_{KK}$ and the Aharonov-Bohm (AB) phase $\theta_H$ in the fifth dimension; $m_{KK} \sim 1350 GeV/(sin \theta_H)^{0.787}$. The cubic and quartic self-couplings of the Higgs boson become smaller than those in the standard model (SM), having universal dependence on $\theta_H$. The decay rates H -> \gamma \gamma, gg are evaluated by summing contributions from KK towers. Corrections coming from KK excited states are finite and about 0.2% (2%) for $\theta_H= 0.12 (0.36)$, branching fractions of various decay modes of the Higgs boson remaining nearly the same as in the SM. The signal strengths of the Higgs decay modes relative to the SM are $\sim cos^2 \theta_H$. The mass of the first KK $Z$ is predicted to be $5.9 (2.4)$TeV for $\theta_H= 0.12 (0.36)$. We also point out the possible enhancement of $\Gamma(H -> \gamma\gamma)$ due to the large $U(1)_X$ charge of new fermion multiplets.