The effective potential for the Aharonov-Bohm phase $theta_H$ in the fifth dimension in GUT inspired $SO(5)times U(1) times SU(3)$ gauge-Higgs unification is evaluated to show that dynamical electroweak symmetry breaking takes place with $theta_H ot= 0$, the 4D Higgs boson mass 125$,$GeV being generated at the quantum level. The cubic and quartic self-couplings $(lambda_3, lambda_4)$ of the Higgs boson are found to satisfy universal relations, i.e. they are determined, to high accuracy, solely by $theta_H$, irrespective of values of other parameters in the model. For $theta_H=0.1$ ($0.15$), $lambda_3$ and $lambda_4$ are smaller than those in the standard model by 7.7% (8.1%) and 30% (32%), respectively.
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