  Theories with extra dimensions of inverse TeV size (or larger) predict a
multitude of signals which can be searched for at present and future colliders.
In this paper, we review the different phenomenological signatures of a
particular class of models, universal extra dimensions, where all matter fields
propagate in the bulk. Such models have interesting features, in particular
Kaluza-Klein (KK) number conservation, which makes their phenomenology similar
to that of supersymmetric theories. Thus, KK excitations of matter are produced
in pairs, and decay to a lightest KK particle (LKP), which is stable and weakly
interacting, and therefore will appear as missing energy in the detector
(similar to a neutralino LSP). Adding gravitational interactions which can
break KK number conservation greatly expands the class of possible signatures.
Thus, if gravity is the primary cause for the decay of KK excitations of
matter, the experimental signals at hadron colliders will be jets + missing
energy, which is typical of supergravity models. If the KK quarks and gluons
decay first to the LKP, which then decays gravitationally, the experimental
signal will be photons and/or leptons (with some jets), which resembles the
phenomenology of gauge mediated supersymmetry breaking models.
