Kaluza-Klein Effects on Higgs Physics in Universal Extra Dimensions

We examine the virtual effects of Kaluza-Klein (KK) states on Higgs physics in universal extra dimension models. We study the partial widths $\Gamma_{h \to gg}$, $\Gamma_{h \to \gamma \gamma}$, and $\Gamma_{h \to \gamma Z}$, which are relevant for Higgs production and detection in future collider experiments. These interactions occur at one loop in the Standard Model, as do the KK contributions. We find that the deviations induced by the KK exchanges can be significant; for one extra dimension, the $gg \to h$ production rate is increased by $10$ for the mass of the first KK state in the range $500 \gsim m_1 \gsim 1500$ GeV, a region untested by current direct search and precision measurement constraints. The $h \to \gamma \gamma$ decay width is decreased by $\lsim 20$ in the same mass range. For two or more universal extra dimensions the results are cutoff dependent, and can only be qualitatively estimated. We comment on the detectability of these shifts at the LHC and at future $e^+ e^-$ and $\gamma \gamma$ colliders.