Heavy Neutral Lepton searches at ATLAS

A summary of searches for heavy neutral leptons (HNLs) at the ATLAS experiment at the Large Hadron Collider is presented. This includes partial and full Run 2 rare $W$ decay searches through lepton number violation and displaced vertices alongside $WW$ scattering events. The searches for HNLs consider lepton number violating decays of the $W$ bosons. Additionally, the contributions of HNLs in $WW$ scattering are taken into account. This includes the first experimental test for a mixed-flavour Weinberg operator, denoted as $C^{(5)}_{e\mu}$. Furthermore, mixed-flavour HNL masses are explored at the TeV scale. No significant excesses are seen, and 95\% CL limits are set in first- and second-generation mixing matrix elements for HNL masses between 2 GeV and 20 TeV.