Cosmological signals of dark matter semi-annihilation

The growth of primordial density fluctuations in the early Universe leads to an inhomogeneous dark matter distribution at high redshift, where semi-annihilation processes of the form $\chi \chi \to {\chi }^c\nu$ can occur with a sizable rate. Using a state-of-the-art model for the cosmological boost factor, we compute the resulting redshift-dependent flux of boosted dark matter particles generated by semi-annihilation, and we study the implications of the boosted component for structure formation and direct detection experiments. We find that the cosmological contribution can enhance the sensitivity of current dark matter searches by up to three orders of magnitude, and may allow future experiments to probe scattering cross sections in the femtobarn range for dark matter masses between $\sim 10$ MeV and $\sim 1$ GeV.