Universal extra dimensions and the Higgs boson mass

We study the combined constraints on the compactification scale 1/R and the Higgs boson mass mH in the standard model with one or two universal extra dimensions. Focusing on precision measurements and employing the Peskin-Takeuchi S and T parameters, we analyze the allowed region in the (mH,1/R) parameter space consistent with current experiments. For this purpose, we calculate complete one-loop KK mode contributions to S, T, and U, and also estimate the contributions from physics above the cutoff of the higher-dimensional standard model. A compactification scale 1/R as low as 250 GeV and significantly extended regions of mH are found to be consistent with current precision data