Constraints on Universal Extra Dimension models with gravity mediated   decays from ATLAS diphoton search
  We discuss the collider phenomenology of Universal Extra Dimension models with gravity mediated decays. We concentrate on diphoton associated with large missing transverse energy signature. At the collider, level-1 Kaluza-Klein (KK) particles are produced in pairs due to the conservation of KK-parity. Subsequently, KK-particles decay via cascades involving lighter KK-particles until reaching the lightest KK-particle (LKP). Finally, gravity induced decay of the LKP into photons gives rise to the diphoton signature. The search for diphoton events with large missing transverse energy was recently communicated by the ATLAS collaboration for 7 TeV center-of-mass energy and 3.1 inverse femtobarn integrated luminosity of the Large Hadron Collider. Above the Standard Model background prediction, no excess of such events was reported. We translate the absence of any excess of the diphoton events to constrain the model parameters, namely, the radius of compactification (R) and the fundamental Planck mass ($M_D$). 
Kirtiman Ghosh and Katri Huitu (Helsinki Institute of Physics)
hep-ph