Search for dark matter particle interactions with electron final states with DarkSide-50

We present a search for dark matter particles with sub-GeV/c^2 masses whose interactions have final state electrons using the DarkSide-50 experiment's (12306 ± 184) kg d low-radioactivity liquid argon exposure. By analyzing the ionization signals, we exclude new parameter space for the dark matter-electron cross section σ̅_e, the axioelectric coupling constant g_Ae, and the dark photon kinetic mixing parameter κ. We also set the first dark matter direct-detection constraints on the mixing angle |U_e4|^2 for keV sterile neutrinos.