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 Γ_hh→_gg,Γ_h→_yy, and and Γ_h→_yz,, 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 →h production rate is increased by 10% -85% for the meass of the first KK state in the range 500 ≳ m₁500 GeV, a region untested by current direct search and precision measurement constraints. The h → 77 decay width is decreased by ≲ 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 yy colliders.