Sensitivity of direct detection experiments to neutrino dark radiation from dark matter decay and a modified neutrino-floor

In this work we analyse the ultimate sensitivity of dark matter direct detection experiments to 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. 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. In the former case, this lifts the “neutrino floor” for xenon-based experiments.