Probes of universal extra dimensions at colliders

In the universal extra dimensions model of Appelquist, Cheng, and Dobrescu, all of the standard model fields are placed in the bulk and thus have Kaluza-Klein (KK) excitations. These KK states can only be pair produced at colliders due to the tree-level conservation of the KK number, with the lightest of them being stable and possibly having a mass as low as $\simeq 350–400\hspace{0.5em}\mathrm{GeV}.$ After calculating the contribution to $g-2$ in this model we investigate the production cross sections and signatures for these particles at both hadron and lepton colliders. We demonstrate that these signatures critically depend upon whether the lightest KK states remain stable or are allowed to decay by any of a number of new physics mechanisms. These mechanisms which induce KK decays are studied in detail.