tt resonance searches and rare decays

In this contribution an overview is given of the ATLAS potential for the discovery of beyond the Standard Model physics through an analysis of signatures related to top quarks. In particular, two specific studies are discussed: - the search for rare decays of the top quark involving flavour-changing neutral currents. ATLAS is expected to improve significantly on the limits on branching ratios for decays t-> qX, where X is a gluon, photon or Z-boson. - the search for resonant decays of beyond-the-standard-model particles into a pair of a top and anti-top quark. Several models predict observable signal even with a limited integrated luminosity. To further improve the ATLAS sensitivity to these signals dedicate high pT top reconstruction algorithms are being developed.