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Abstract

This letter presents a combination of searches for Higgs boson pair production using up to 36.1 fb$^{-1}$ of proton-proton collision data at a centre-of-mass energy $\sqrt{s} = 13$ TeV recorded with the ATLAS detector at the LHC. The combination is performed using six analyses searching for Higgs boson pairs decaying into the bbbb, bbWW, bb$\tau\tau$, WWWW, bb$\gamma \gamma$ and WW$\gamma\gamma$ final states. Results are presented for non-resonant and resonant Higgs boson pair production modes. The combined observed limit at 95% confidence level on the non-resonant Higgs boson pair production cross-section is 6.9 times the predicted Standard Model cross-section. Limits are also set on the ratio ($\kappa_{\lambda}$) of the Higgs boson self-coupling to its Standard Model value. This ratio is constrained at 95% confidence level to $-5.0 < \kappa_{\lambda} <12.0$. In addition, limits are set on the production of narrow scalar resonances and spin-2 Kaluza-Klein Randall-Sundrum gravitons. Exclusion regions are also provided in the parameter space of the habemus Minimal Supersymmetric Standard Model and the Electroweak Singlet Model.