Minimal Freeze-in Dark Matter: Reviving electroweak doublet dark matter with Boltzmann suppressed freeze-in

Abstract

Dark matter communicating with the Standard Model solely via electroweak interactions provides a compelling picture. However, thermal freeze-out of electroweak doublet dark matter is generically strongly excluded by direct detection. We show that SU(2)${}_L$ doublet fermion dark matter evades direct detection if its mass exceeds $10^{10}$ GeV. If the neutral Dirac fermion is split into a pseudo-Dirac pair (via high dimension operator) this limit can be relaxed to 300 GeV. Provided the dark matter mass is above the reheat temperature of the Universe, the production rate never exceeds the Hubble rate in cases of interest, thus the dark matter never thermalizes. We apply constraints from direct detection (e.g. LZ) and consider the discovery potential of Darwin. This scenario presents the most minimal model of freeze-in dark matter, and is both elegant and highly predictive.