Warm Dark Matter Doorframe for Light Dark Matter Direct Detection Experiments

Future low-threshold direct detection experiments can be sensitive to dark matter with mass below MeV. If such light dark matter has been in sufficient thermal contact with the visible sector in the early universe, the thermal motion inherited from Standard Model particles will cause significant free-streaming effect similar to the thermal warm dark matter model. The free-streaming effect is subject to the structure formation constraint from astrophysical observations. I will discuss when identifying the interaction responsible for the thermal contact to be the interaction probed by dark matter direct detection experiments, recasting the current warm dark matter bound gives a constraint on light dark matter parameter region for future direct detection experiments.