Cosmic-ray upscattered inelastic dark matter

Light non-relativistic components of the galactic dark matter halo elude direct detection constraints because they lack the kinetic energy to create an observable recoil. However, cosmic-rays can upscatter dark matter to significant energies, giving direct detection experiments access to previously unreachable regions of parameter-space at very low dark matter mass. In this work we extend the cosmic-ray dark matter formalism to models of inelastic dark matter and show that previously inaccessible regions of the mass-splitting parameter space can be probed. Conventional direct detection of non-relativistic halo dark matter is limited to mass splittings of $\delta\sim10~\mathrm{keV}$ and is highly mass dependent. We find that including the effect of cosmic-ray upscattering can extend the reach to mass splittings of $\delta\sim100~\mathrm{MeV}$ and maintain that reach at much lower dark matter mass.