WMAP7 and future CMB constraints on annihilating dark matter: implications for GeV-scale WIMPs

Aims. We calculate constraints from current and future cosmic microwave background (CMB) measurements on annihilating dark matter (DM) with masses below the electroweak scale: mDM = 5 − 100 GeV. In particular, we assume the S-wave annihilation mode to be dominant, and focus our attention on the lower end of this mass range, as DM particles with masses mDM ~ 10 GeV have recently been claimed to be consistent with the CoGeNT and DAMA/LIBRA results, while also providing viable DM candidates to explain the measurements of Fermi and WMAP haze. We study the model (in)dependence of the CMB power spectra on particle physics DM models, large-scale structure formation and cosmological uncertainties. We attempt to find a simple and practical recipe for estimating current and future CMB bounds on a broad class of DM annihilation models.