  Universal extra dimensions, presumably observable at some high-energy scale,
would modify low-energy observables, being particularly relevant for physical
processes forbidden at tree level by the Standard Model. We address the
Kaluza-Klein contributions from the 5-dimensional Standard Model to the
anomalous magnetic moment and to branching ratios of electromagnetic decays of
the top quark. In accordance with present bounds on the compactification scale,
contributions to both quantities are found to be at least 3 orders of magnitude
below Standard-Model predictions.
