Dark matter search with CMB: a study of foregrounds

The energy injected from dark matter annihilation and decay processes potentially raises the ionisation of the intergalactic medium and leaves visible footprints on the anisotropy maps of the cosmic microwave background (CMB). Galactic foregrounds emission in the microwave bands contaminate the CMB measurement and may affect the search for dark matter's signature. In this paper, we construct a full CMB data and foreground simulation based on the design of the next-generation ground-based CMB experiments. The foreground residual after the components separation on maps is fully considered in our data analysis, accounting for various contamination from the emission of synchrotron, thermal dust, free-free and spinning dust. We analyse the corresponding sensitivity on dark matter parameters from the temperature and polarization maps, and we find that the CMB foregrounds leave a non-zero yet controllable impact on the sensitivity. Comparing with statistics-only analysis, the CMB foreground residual leads to a factor of at most 19% weakening on energy-injection constraints, depending on the specific dark matter process and experimental configuration. Strong limits on dark matter annihilation rate and decay lifetime can be expected after foreground subtraction.