New results on $t\bar{t}W$ and $t\bar{t}t\bar{t}$ production with the ATLAS experiment

The top-quark pair production in association with a W boson ($t\bar{t}W$) is an interesting process as it allows the study of $q\bar{q}$ vs $gg$ initiated $t\bar{t}$ production and is an important background to processes like $t\bar{t}H$ or $t\bar{t}t\bar{t}$ production. Due to higher order electroweak corrections, this process is difficult to model. A difference between the measured and the predicted value for $t\bar{t}W$ production rate has been observed in previous analyses. To improve our understanding of this process, a new inclusive and differential measurement of this process in events with multiple leptons in the final state was performed. Also, a ratio of $t\bar{t}W$ events with a positively and a negatively charged W-boson was measured. Another challenging final state is the production of four top quarks ($t\bar{t}t\bar{t}$). While the previous result using full run 2 dataset in the two same-sign charge and three lepton channel already allowed to obtain evidence of this process, a re-analysis of this dataset with several modifications allowed to observe this process. In addition to the measurement of the $t\bar{t}t\bar{t}$ cross-section, limits are set on the production of three top quarks as well as on the CP properties of the top Yukawa coupling and on EFT operator coefficients affecting the $t\bar{t}t\bar{t}$ production.