Missing Energy Signal in tt to Probe Large Extra Dimensions

The discovery of a light Higgs boson has made the hierarchy problem in the Standard Model of electroweak interactions more immediate. Among the new physics solutions proposed for this is a model with large extra dimensions, which, among other things, predicts a tower of invisible, massive graviton Kaluza-Klein (KK) modes, leading to characteristic missing energy-momentum signals at a collider. We have studied production of graviton KK modes in association with tt pairs at high energy e+e- colliders, takimg into account the different decay modes of the top quark, as well as the possibility of top-jet tagging at high energies. Preliminary studies show that the missing energy component in these signals could help us probe significantly higher values of the string scale MS that have been achieved till now.