  The regime of dark matter (DM) freeze-in at stronger coupling interpolates
between freeze-in and freeze-out. It relies on Boltzmann-suppressed dark matter
production, implying that the Standard Model bath temperature never exceeds the
dark matter mass. In this work, we study this regime in the context of sterile
neutrino dark matter, which can be sufficiently long-lived for a tiny
sterile-active mixing. The sterile neutrino is assumed to couple to a real
singlet scalar, providing for a thermal production mechanism of the former. We
find that DM mass can range from GeV to tens of TeV consistently with all the
constraints. The most interesting aspect of the consequent freeze-in
phenomenology is that the sterile neutrino dark matter can be probed
efficiently by both direct detection experiments and invisible Higgs decay at
the LHC.
