Direct detection of Sub-GeV Dark Matter via 3-body Inelastic Scattering Process

Direct detection of Sub-GeV dark matter (DM) is challenging because the recoil energy of the nuclei or electron from the elastic scattering of a sub-GeV DM off the target can hardly reach the detector threshold. In this paper, we present a new direct detection strategy for sub-GeV DM via the three-body inelastic scattering process, $\chi + \chi + {\rm SM} \to \eta + {\rm SM}$,where$\chi$isDMcandidateand$\eta $ is either a DM composite state or any dark radiation. This process is common for a large class of DM models without presuming particular thermal history in the early Universe. The typical signature from this process is almost a monoenergetic pulse signal where the recoil energy comes from either the binding energy or the consumed DM particle. We show that detectable DM mass range can be effectively enlarged compared to the elastic scattering process.