Search for exotic particles in multileptonic final states with the ATLAS detector

The search for exotic particles Beyond the Standard Model (BSM) is a major part of the ATLAS physics program. Due to the low number of Standard Model events in final states with large lepton multiplicity, searches in these final states allow to reject a substantial fraction of background providing a better signal-to-noise ratio. New physics (NP) events are searched for in several processes: production of doubly charged Higgs bosons (H-+/-+/-) and production of heavy neutral or charged leptons predicted, for instance in mechanisms like Type-III SeeSaw or LRSM models. BSM searches in multileptonic finale states using the pp collision data sample collected in the Run2 by the ATLAS experiment corresponding to 80.0 fb(-1) of integrated luminosity at a centre-of-mass energy of 13 TeV are presented. Final states with same-sign leptons (only electrons and muons) are particularly interesting since they are affected by low Standard Model background. Searches are performed in final states which maximize the predicted production cross-section.