Search for new physics in final states with leptons with ATLAS

One of the main goals in the physics program of the ATLAS experiment at Large Hadron Collider is to discover hints for extensions to the Standard Model. Leptons provide experimentally clear signatures in the new physics searches with the ATLAS detector. This paper presents results of three new physics searches in final states characterized by leptons: a search for pair production of heavy leptons belonging to a new $SU(2)_{\rm L}$ triplet which is predicted by the type-III seesaw mechanism; a search for a new charged heavy gauge boson resonance ($W'$) decaying into a charged lepton and a neutrino; and a search for lepton-flavor violating decays of $Z$ bosons into a $\tau$-lepton and an electron or a muon. They are based on 36.1-79.8$~{\rm fb^{-1}}$ of $pp$ collision data recorded by the ATLAS detector at $\sqrt{s}=13~{\rm TeV}$. No statistically significant excess from the Standard Model expectation has been observed and upper limits for various new physics models have been set as the interpretation of the results.