Searches for BSM multi-top production in same-sign dilepton and multilepton final states with the ATLAS Experiment

The Standard Model (SM) four-top-quark (4-top) production has been observed with almost twice the signal strength in the ATLAS experiment. In addition, the four-top shows a very large correlation with the three-top (3-top) production given the similar final states. The multi-top (4-top and 3-top) processes can be enhanced in several beyond SM (BSM) scenarios or stronger Higgs-Top Yukawa coupling. A new search for the BSM 3-top and 4-top processes are being performed with the full Run-2 and partial Run-3 data in ATLAS, including the heavy Higgs boson production from additional Higgs sector and the top-philic resonance production associated with a top-quark pair (ttH/A and ttZ'). The analysis focuses on the same-sign dilepton and multilepton final states, which helps to reduce the background rate. In this iteration, new background estimation approaches are being studied, based on the successful data-driven method for the ttW background in the SM 4-top observation. Novel multivariate analysis techniques such as the Graph Neural Network (GNN) and Transformer will also be utilized to improve the signal sensitivities and background estimations. In addition, modeling and classification of the 3-top processes, which are rare but highly sensitive to the BSM signatures, is one of the targets in this analysis.