Search for direct top squark pair production and dark matter production in final states with two leptons in $\sqrt{s} = 13$ TeV $pp$ collisions using 13.3 fb$^{-1}$ of ATLAS data

The results of a search for new phenomena in events with two leptons (electrons or muons) are reported, using 13.3 fb$^{-1}$ of integrated luminosity from LHC $pp$ collisions at $\sqrt{s}=13$ TeV collected by the ATLAS detector. Three possible signals are targeted by dedicated selections: the pair production of top squarks decaying via the three body mode $\tilde{t}_{1} \rightarrow \tilde{\chi}^{0}_{1} W b$; the pair production of top squarks decaying via $\tilde{t}_{1} \rightarrow \tilde{\chi}^{\pm}_{1} b \rightarrow \tilde{\chi}^{0}_{1} W^{(*)} b$; and the production of dark matter in association with a $t\bar{t}$ pair. No excess above the Standard Model expectation is observed, and exclusion limits at 95% confidence level are derived for the different models.