Search for new physics involving top quarks at ATLAS

We present a search for anomalous missing transverse energy in the lepton+jetstt final state. Such a phenomenon can arise from a number of Standard Model extensions, but we focus here on a search for a pair-produced top partner decaying to a top quark and a long livedneutral particle which escapes undetected. We report the results of the search for FCNC processes in top quark decay as well as in top quark production in proton-proton collisions at sqrt(s)=7 TeV, recorded with the ATLAS detector during 2010. We present results obtained in the lepton+jets and dilepton channels, with emphasis on the current understanding of the systematic uncertainties.