Universal Extra Dimensions at the e-e- Colliders
  Universal Extra Dimensions (UEDs) with compactification radius near the TeV scale provide interesting phenomenology at future colliders. The collider signals of the first Kaluza-Klein (KK) level are very similar to those of a supersymmetric model with a nearly degenerate superpartner spectrum. The heavier first level KK states cascade decay to the lightest KK particles (LKP), which is neutral and stable because of KK-parity. The signatures involve missing energy and relatively soft jets and leptons which can be difficult for detection. The KK electron signal in $e^- e^-$ collisions is free from the problematic two photon background therefore provides a unique opportunity for a detailed studies of the KK electrons in the Universal Extra Dimension scenario. 
Hsin-Chia Cheng