Combination of Searches for Resonant Higgs Boson Pair Production Using $pp$ Collisions at $\sqrt{s}=13\text{}\text{}\mathrm{TeV}$ with the ATLAS Detector

A combination of searches for a new resonance decaying into a Higgs boson pair is presented, using up to $139\text{}\text{}{\mathrm{fb}}^{-1}$ of $pp$ collision data at $\sqrt{s}=13\text{}\text{}\mathrm{TeV}$ recorded with the ATLAS detector at the LHC. The combination includes searches performed in three decay channels: $b\overline{b}b\overline{b}$, $b\overline{b}{\tau }^{+}{\tau }^{-}$, and $b\overline{b}\gamma \gamma $. No excess above the expected Standard Model background is observed and upper limits are set at the 95% confidence level on the production cross section of Higgs boson pairs originating from the decay of a narrow scalar resonance with mass in the range 251 GeV–5 TeV. The observed (expected) limits are in the range 0.96–600 fb (1.2–390 fb). The limits are interpreted in the type-I two-Higgs-doublet model and the minimal supersymmetric standard model, and constrain parameter space not previously excluded by other searches.