CMB constraints on dark matter models with large annihilation cross section

The injection of secondary particles produced by dark matter (DM) annihilation around redshift $\sim 1000$ would inevitably affect the process of recombination, leaving an imprint on cosmic microwave background (CMB) anisotropies and polarization. We show that the most recent CMB measurements provided by the WMAP satellite mission place interesting constraints on DM self-annihilation rates, especially for models that exhibit a large Sommerfeld enhancement of the annihilation cross section, as recently proposed to fit the PAMELA and ATIC results. Furthermore, we argue that upcoming CMB experiments such as Planck, will improve the constraints by at least 1 order of magnitude, thus providing a sensitive probe of the properties of DM particles.