Probing Light Inelastic Dark Matter from Direct Detection

Different dark matter (DM) candidates could have different types of DM-leptonand/or DM-quark interactions. For direct detection experiments, this leads todiversity in the recoil spectra, where both DM-electron and DM-nucleusscatterings may contribute. Furthermore, kinematic effects such as those of theinelastic scattering can also play an important role in shaping the recoilspectra. In this work, we systematically study signatures of the lightexothermic inelastic DM from the recoil spectra including both the DM-electronscattering and Migdal effect. Such inelastic DM has mass around (sub-)GeV scaleand the DM mass-splitting ranges from 1keV to 30keV. We analyze the directdetection sensitivities to such light inelastic DM. For different inelastic DMmasses and mass-splittings, we find that the DM-electron recoil and Migdaleffect can contribute significantly and differently to the direct detectionsignatures. Hence, it is important to perform combined analysis to include boththe DM-electron recoil and Migdal effect. We further demonstrate that thisanalysis has strong impacts on the cosmological and laboratory bounds for theinelastic DM.