Searches for resonances decaying into Higgs boson pairs with the ATLAS Experiment

This document summarizes recent searches for heavy resonances (X) decaying into pairs of Higgs bosons (HH) or a new scalar plus a Higgs boson (SH) using data from the ATLAS experiment at the Large Hadron Collider. The analyses utilize the full Run-2 data and, in some cases, partial Run-3 data, targeting various final states including $bb\tau\tau$, $bb\gamma\gamma$, $4b$, and $6b$. No significant excess over the Standard Model prediction is observed. Stringent upper limits are set on the production cross-section times branching ratio for a wide range of resonance masses and for various benchmark models. These results represent a significant improvement in sensitivity over previous searches.