Closer look at CMB constraints on WIMP dark matter

We use cosmic microwave background data from the WMAP, SPT, BICEP, and QUaD experiments to obtain constraints on the dark matter particle mass m(chi), and show that the combined data requires m(chi) > 7.6 GeV at the 95% confidence level for the chi chi -> b (b) over bar channel assuming s-wave annihilation and a thermal cross section <sigma(a)v > = 3 x 10(-26) cm(3)/s. We examine whether the bound on m(chi) is sensitive to sigma(8) measurements made by galaxy cluster observations. The large uncertainty in sigma(8) and the degeneracy with Omega(m) allow only small improvements in the dark matter mass bound. Increasing the number of effective neutrinolike degrees of freedom to N-eff = 3.85 improves the mass bound to m(chi) > 8.6 GeV at 95% confidence, for the chi chi -> b (b) over bar channel. We also study models in which dark matter halos at z < 60 reionize the Universe. We compute the Ostriker-Vishniac power resulting from partial reionization at intermediate redshifts 10 < z < 60, but find the effect to be small. We discuss the importance of the large angle polarization as a complementary probe of dark matter annihilation. By performing Monte Carlo simulations, we show that future experiments that measure the EE power spectrum from 20 < l < 50 can exclude m(chi) similar to 10 GeV at the 2(3)sigma level provided the error bars are smaller than 4(3) x cosmic variance. We show that the Planck experiment will significantly improve our knowledge of dark matter properties.