Abstract

The top quark is the most massive known fundamental particle, although the reason for its large mass is not fully understood. Due to its unique properties, the top quark is potentially sensitive to effects of new physics beyond the Standard Model. It is crucial, therefore, to perform precision measurements of top-quark properties and couplings in order to test the Standard Model and search for these hints. This is becoming possible with the unprecedented amount of data provided by the second operational run of the Large Hadron Collider and with the substantial dataset collected by the ATLAS experiment, we can now start to measure very rare cross-sections. I will present the recent ATLAS measurement of the production of four top quarks in the final state. Results for the coupling of top quarks with additional bosons (W, Z and H) will also be discussed and possible enhancements of very rare SM cross-sections from new physics through the production of heavy objects in association with a top-quark pair will be briefly explored.