  In this work we analyse the ultimate sensitivity of dark matter direct
detection experiments, the "neutrino-floor", in the presence of anomalous
sources of dark radiation in form of SM or semi-sterile neutrinos. This
flux-component is assumed to be produced from dark matter decay. Since dark
radiation may mimic dark matter signals, we perform our analysis based on
likelihood statistics that allows to test the distinguishability between
signals and backgrounds. We show that the neutrino floor for xenon-based
experiments may be lifted in the presence of extra dark radiation. In addition,
we explore the testability of neutrino dark radiation from dark matter decay in
direct detection experiments. Given the previous bounds from neutrino
experiments, we find that xenon-based dark matter searches will not be able to
probe new regions of the dark matter progenitor mass and lifetime parameter
space when the decay products are SM neutrinos. In turn, if the decay instead
happens to a fourth neutrino species with enhanced interactions to baryons, DR
can either constitute the dominant background or a discoverable signal in
direct detection experiments.
