Searches for rare and invisible Higgs boson decays and for high-mass resonances with the ATLAS detector

<!--HTML--><p><span style="color:#000000">A first talk presents two new ATLAS results on searches for rare and invisible decays of the Higgs boson using the full LHC Run-2 dataset. The as-yet unobserved decay of a Higgs boson to Zγ is searched for in the final state with 2 leptons (e or μ) and a photon.&nbsp; Higgs boson decays to invisible particles, as predicted by a number of models beyond the Standard Model, are searched for in the vector-boson fusion production mode. Such a signature could for example arise if the Higgs boson couples directly to dark matter particles.</span><br /> <span style="color:#000000">In a second talk two new results on searches for high mass resonances in VV and ttbar final stated are presented. At resonance masses well above 1 TeV, these searches face specific challenges and employ new identification techniques to disentangle collimated decay products in highly boosted configurations. In addition to benefiting from the larger dataset, the discovery potential of these analyses has been improved by developing novel object tagging techniques&nbsp; and by using improved background estimation methods.<span> </span></span></p>