Search for scalar dark energy in $t\bar{t}+E_{T}^{\text{miss}}$ and mono-jet final states with the ATLAS detector

This note presents the first collider search for light scalar particles that could contribute to the accelerating expansion of the observable universe. The results are based on a re-interpretation of a search for top super-partners using the $t\bar{t}+E_{T}^{\text{miss}}$ signature and a search for dark matter using the mono-jet signature. The analysis uses a dataset of LHC $pp$ collision events collected with the ATLAS detector at $\sqrt{s}=13$ TeV corresponding to an integrated luminosity of 36.1~fb$^{-1}$. No significant excess over the predicted background is observed. The search allows to set the most stringent constraints on the suppression scale of conformal and disformal couplings of dark energy to standard model matter in the context of an effective field theory of dark energy.