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 $\pm$ 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 ${\bar{\sigma }}_e$, the axioelectric coupling constant $g_{Ae}$, and the dark photon kinetic mixing parameter $\kappa$. We also set the first dark matter direct-detection constraints on the mixing angle ${\mid U_{e4}\mid }^2$ for keV sterile neutrinos.